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 ==========Studies that Confirm the Abortion-Breast Cancer Link========== ==========Studies that Confirm the Abortion-Breast Cancer Link==========
  
-Ecological epidemiological studies use gross vital-statistic-like data, such as the incidence of breast cancer or abortions in a county, state, or country. Patients are not interviewed,​ and hospital records are not examined. ​+[[studies_on_the_abortion-breast_cancer_link|Ecological epidemiological studies]] use gross vital-statistic-like data, such as the incidence of breast cancer or abortions in a county, state, or country. Patients are not interviewed,​ and hospital records are not examined. ​
  
-Two ecological epidemiological studies, the 1989 Remennick Study and the 2007 Carroll Study, show a strong association between induced abortion and breast cancer. Another 19 epidemiological studies show some relationship between induced abortion and breast cancer. These 19 studies occur across diverse countries and cultures—from Japan and China, to Iran and Armenia, to Germany and the United States. They are organized chronologically and (loosely) in order of increasing statistical and methodological sophistication.+Two ecological epidemiological studies, the [[studies_on_the_abortion-breast_cancer_link|1989 Remennick Study]] and the 2007 Carroll Study, show a strong association between induced abortion and breast cancer. Another 19 epidemiological studies show some relationship between induced ​[[abortion-breast_cancer_link|abortion and breast cancer]]. These 19 studies occur across diverse countries and cultures—from Japan and China, to Iran and Armenia, to Germany and the United States. They are organized chronologically and (loosely) in order of increasing statistical and methodological sophistication.
  
 =====1. 1989 Remennick Study===== =====1. 1989 Remennick Study=====
  
-Larissa Remennick’s 1989 study of breast and cervical cancers in the USSR showed a “consistent association between abortion rates…and incidence of both breast and cervical cancers.”((Larissa I. Remennick, “Reproductive Patterns and Cancer Incidence in Women: A Population-Based Correlation Study in the USSR,” //​International Journal of Epidemiology//​ 18, no. 3 (September 1989): 498-510.)) The author notes that abortions exceeded live births in the years following abortion’s legalization in 1955, due to the procedure’s use as the nation’s primary means of birth control.+Larissa Remennick’s ​[[studies_on_the_abortion-breast_cancer_link|1989 study]] of breast and cervical cancers in the USSR showed a “consistent association between abortion rates…and incidence of both breast and cervical cancers.”((Larissa I. Remennick, “Reproductive Patterns and Cancer Incidence in Women: A Population-Based Correlation Study in the USSR,” //​International Journal of Epidemiology//​ 18, no. 3 (September 1989): 498-510.)) The author notes that abortions exceeded live births in the years following abortion’s legalization in 1955, due to the procedure’s use as the nation’s primary means of birth control.
  
 **__Induced abortion.__** Remennick found that, overall, the induced abortion rate was the fourth-ranked variable in determining age-adjusted breast cancer incidence (after cumulative fertility rate, early marriage prevalence, and early age at first birth prevalence). This finding is remarkable given the small percentage of women aborting in primigravidas (that is, aborting their first pregnancies) and given that all induced abortions here are aggregated and not parsed out (e.g., by their timing related to first full-term pregnancy). However, the very fact that a small percentage of women aborted in primigravidas provides a clear picture of the potential effects of repeated abortions, even when they take place after full-term pregnancy. **__Induced abortion.__** Remennick found that, overall, the induced abortion rate was the fourth-ranked variable in determining age-adjusted breast cancer incidence (after cumulative fertility rate, early marriage prevalence, and early age at first birth prevalence). This finding is remarkable given the small percentage of women aborting in primigravidas (that is, aborting their first pregnancies) and given that all induced abortions here are aggregated and not parsed out (e.g., by their timing related to first full-term pregnancy). However, the very fact that a small percentage of women aborted in primigravidas provides a clear picture of the potential effects of repeated abortions, even when they take place after full-term pregnancy.
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 =====2. 2007 Carroll Study===== =====2. 2007 Carroll Study=====
  
-**__Induced abortion.__** In 2007, actuary Patrick Carroll found,​((Patrick S. Carroll, “The Breast Cancer Epidemic: Modeling and Forecasts Based on Abortion and Other Risk Factors,” //Journal of American Physicians and Surgeons// 12, no. 3 (2007): 72-78. )) with an empirical model that he built from English and Welsh data, that of the four reproductive risk factors he tested, the greatest predictor of future breast cancer incidence was a nation’s abortion rate. Nulliparous abortions, in particular, were significant in determining breast cancer rates.+**__Induced abortion.__** In 2007, actuary ​[[abortion-breast_cancer_link|Patrick Carroll found]],((Patrick S. Carroll, “The Breast Cancer Epidemic: Modeling and Forecasts Based on Abortion and Other Risk Factors,” //Journal of American Physicians and Surgeons// 12, no. 3 (2007): 72-78. )) with an empirical model that he built from English and Welsh data, that of the four reproductive risk factors he tested, the greatest predictor of future breast cancer incidence was a nation’s abortion rate. Nulliparous abortions, in particular, were significant in determining breast cancer rates.
  
-Carroll also found that falling fertility affected the incidence of breast cancer. Using national abortion, fertility, and breast cancer registries, Carroll made predictions regarding breast cancer rates in nine European countries (England, Wales, Scotland, Northern Ireland, the Irish Republic, Sweden, the Czech Republic, Finland, and Denmark).+Carroll also found that falling fertility affected the [[biology_of_the_abortion-breast_cancer_link|incidence of breast cancer]]. Using national abortion, fertility, and breast cancer registries, Carroll made predictions regarding breast cancer rates in nine European countries (England, Wales, Scotland, Northern Ireland, the Irish Republic, Sweden, the Czech Republic, Finland, and Denmark).
  
 =====3. 1957 Segi Study===== =====3. 1957 Segi Study=====
  
-The first epidemiologic study examining breast cancer and abortion was published in 1957 in Japan.((M. Segi, I. Fukushima, S. Fujisaku, M. Kurihara, S. Saito, K. Asano, and M. Kamoi, “An Epidemiological Study on Cancer in Japan,” //Japanese Journal of Cancer Research (GANN)// 48 (Suppl.) (1957): 1-63. )) As the study is writtenwith data broken down by number of pregnancy outcomes (e.g., induced abortion, miscarriage),​ rather than by women experiencing these outcomesthe results are not comparable to those of other studies. However, in his 1996 meta-analysis,​ Joel Brind uses other Japanese studies to approximate the average number of induced abortions to which each woman with induced abortion history was exposed.+The first epidemiologic study examining breast cancer and abortion was published in [[studies_on_the_abortion-breast_cancer_link|1957 in Japan]].((M. Segi, I. Fukushima, S. Fujisaku, M. Kurihara, S. Saito, K. Asano, and M. Kamoi, “An Epidemiological Study on Cancer in Japan,” //Japanese Journal of Cancer Research (GANN)// 48(Suppl.) (1957): 1-63.)) As the study is written---with data broken down by number of pregnancy outcomes (e.g., induced abortion, ​[[effects_of_miscarriage_on_breast_cancer_risks|miscarriage]]), rather than by women experiencing these outcomes---the results are not comparable to those of other studies. However, in his 1996 meta-analysis,​ Joel Brind uses other Japanese studies to approximate the average number of induced abortions to which each woman with induced abortion history was exposed.
  
 As Brind notes, the Segi study only includes parous women, and the control population is “slightly older than the patient population,​” but by his estimation, the study shows evidence of a statistically significant increase in the risk of breast cancer among women with a history of induced abortion.((Joel Brind, Vernon M. Chinchilli, Walter B. Severs, and Joan Summy-Long, “Induced Abortion as an Independent Risk Factor for Breast Cancer: A Comprehensive Review and Meta-Analysis,​” //Journal of Epidemiology and Community Health// 50, no. 5 (1996): 483-484.)) As Brind notes, the Segi study only includes parous women, and the control population is “slightly older than the patient population,​” but by his estimation, the study shows evidence of a statistically significant increase in the risk of breast cancer among women with a history of induced abortion.((Joel Brind, Vernon M. Chinchilli, Walter B. Severs, and Joan Summy-Long, “Induced Abortion as an Independent Risk Factor for Breast Cancer: A Comprehensive Review and Meta-Analysis,​” //Journal of Epidemiology and Community Health// 50, no. 5 (1996): 483-484.))
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 =====4. 1981 Pike Study===== =====4. 1981 Pike Study=====
  
-The first U.S. study of abortion and breast cancer in 1981,((M.C. Pike, B.E. Henderson, J.T. Casagrande, I. Rosario, and G.E. Gray, “Oral Contraceptive Use and Early Abortion as Risk Factors for Breast Cancer in Young Women,” //British Journal of Cancer// 43, no. 1 (1981): 72-76.)) which analyzed the history of a total sample of 435 Los Angeles County women, also suggested an increased (though perhaps not significant) risk of breast cancer with induced abortion.+The [[studies_on_the_abortion-breast_cancer_link|first U.S. study]] of abortion and breast cancer in 1981,((M.C. Pike, B.E. Henderson, J.T. Casagrande, I. Rosario, and G.E. Gray, “Oral Contraceptive Use and Early Abortion as Risk Factors for Breast Cancer in Young Women,” //British Journal of Cancer// 43, no. 1 (1981): 72-76.)) which analyzed the history of a total sample of 435 Los Angeles County women, also suggested an increased (though perhaps not significant) risk of breast cancer with induced abortion.
  
-This study is insufficiently randomized, has a small sample, is based on interviews conducted over the telephone, is marked by sampling bias and survivor or health bias, and may suffer from reporting difficulties surrounding abortion law change. Its cases and controls differ across risk factors other than induced abortion, several possible breast cancer risk factors are left out of its analyses, and its analyses are not multiple regressions. Additionally,​ its analysis does not distinguish between induced and spontaneous abortion. Many of these are a consequence of its early, exploratory nature; regardless, this study was a very important step in the development of the field of induced abortion and breast cancer.+This [[common_problems_in_abortion-breast_cancer_studies|study]] is insufficiently randomized, has a small sample, is based on interviews conducted over the telephone, is marked by sampling bias and survivor or health bias, and may suffer from reporting difficulties surrounding abortion law change. Its cases and controls differ across risk factors other than induced abortion, several possible breast cancer risk factors are left out of its analyses, and its analyses are not multiple regressions. Additionally,​ its analysis does not distinguish between induced and spontaneous abortion. Many of these are a consequence of its early, exploratory nature; regardless, this study was a very important step in the development of the field of induced abortion and breast cancer.
  
 The case-control study included 163 white breast cancer patients diagnosed, before the age of 33, between July 1972 and December 1978 and identified through the University of Southern California Cancer Surveillance Program. These cases were matched with 153 neighborhood controls and 119 friend controls. The case-control study included 163 white breast cancer patients diagnosed, before the age of 33, between July 1972 and December 1978 and identified through the University of Southern California Cancer Surveillance Program. These cases were matched with 153 neighborhood controls and 119 friend controls.
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 **__Small sample, limited generalizability,​ unsuitable data collection means.__** Pike’s sample is quite small. That all participants were white would limit the generalizability of the study’s findings. Additionally,​ the interview’s administration over the telephone could diminish any influence of induced abortion through underreporting. **__Small sample, limited generalizability,​ unsuitable data collection means.__** Pike’s sample is quite small. That all participants were white would limit the generalizability of the study’s findings. Additionally,​ the interview’s administration over the telephone could diminish any influence of induced abortion through underreporting.
  
-**__Health or survivor bias.__** Deceased cases were excluded, and this survivor bias may have weakened the demonstrated effect of induced abortion. Furthermore,​ “controls had to be malignancy-free,​” and this health bias may have skewed the demonstrated effect of induced abortion.((If the correlation between induced abortion and breast cancer exists, a univariate bias (throwing out malignant people in the control group) throws out aborting people (in the control group). Because the control group has even fewer abortions now (in proportion to the levels cases exhibit), the statistic shows an even stronger correlation (more effect) between induced abortion and breast cancer: Throwing out malignant controls would bias the effect of induced abortion upward. \\ If there is no correlation between induced abortion and breast cancer, throwing out malignant women would not throw out any extra aborting women (in proportion) in the control group. Aborting women (not being any more likely to be malignant than the other controls) are dropped with the same frequency as the other controls: Throwing out malignant controls would not bias the analysis.)) However, the restriction of the study to women under 33 reduces the likelihood that a very early abortion resulting in breast cancer would eliminate women diagnosed with breast cancer before the start of the study, a problem we discuss in detail above.+**__Health or survivor bias.__** Deceased cases were excluded, and this survivor bias may have weakened the demonstrated effect of induced abortion. Furthermore,​ “controls had to be malignancy-free,​” and this health bias may have skewed the demonstrated effect of induced abortion.((If the correlation between induced abortion and breast cancer exists, a univariate bias (throwing out malignant people in the control group) throws out aborting people (in the control group). Because the control group has even fewer abortions now (in proportion to the levels cases exhibit), the statistic shows an even stronger correlation (more effect) between induced abortion and breast cancer: Throwing out malignant controls would bias the effect of induced abortion upward. \\ If there is no correlation between induced abortion and breast cancer, throwing out malignant women would not throw out any extra aborting women (in proportion) in the control group. Aborting women (not being any more likely to be malignant than the other controls) are dropped with the same frequency as the other controls: Throwing out malignant controls would not bias the analysis.)) However, the restriction of the study to women under 33 reduces the likelihood that a very early abortion resulting in breast cancer would eliminate women diagnosed with breast cancer before the start of the study.
  
-**__Reporting difficulty around abortion law change.__** Following the signing of the 1967 Therapeutic Abortion Act,​((Planned Parenthood Affiliates of California Action Funds, “Issues: History of Abortion Law in California,​” Planned Parenthood Action Funds in California. [[http://​www.ppactionca.org/​issues/​abortion.html]] ​(accessed ​April 18, 2013).  The site notes that the 1967 Therapeutic Abortion Act “[m]ade abortion legal if authorized by a hospital committee that finds the pregnancy will gravely impair a woman’s physical or mental health, or where a local district attorney or court finds probable cause to believe the pregnancy resulted from rape or incest.”)) the data seem to show that the incidence of induced abortion increased markedly.((Wm. Robert Johnston, “Historical ​abortion statistics, California (USA),” Abortion statistics and other data-- Johnston`s Archive, November 21, 2012[[http://​www.johnstonsarchive.net/​policy/​abortion/​usa/​ab-usa-CA.html]] ​(accessed ​April 18, 2013).)) Because of the time frame of this study, and because of the eight to 10 years required for the development of detectable breast cancers, it is likely that some fraction of the women with detectable cases of breast cancer in this sample had legally procured abortions and some women had illegally procured abortions. (All women were residing in Los Angeles County at the time of their diagnosis, but it may be that some did not live in California at the time of their abortion or procured their abortion elsewhere.) It would have been interesting to assess the timing of the induced abortions alongside corresponding breast cancer diagnoses.+**__Reporting difficulty around abortion law change.__** Following the signing of the 1967 Therapeutic Abortion Act,​((Planned Parenthood Affiliates of California Action Funds, “Issues: History of Abortion Law in California,​” ​//Planned Parenthood Action Funds in California//Available at [[http://​www.ppactionca.org/​issues/​abortion.html]]. Accessed ​April 18, 2013.  The site notes that the 1967 Therapeutic Abortion Act “[m]ade abortion legal if authorized by a hospital committee that finds the pregnancy will gravely impair a woman’s physical or mental health, or where a local district attorney or court finds probable cause to believe the pregnancy resulted from rape or incest.”)) the data seem to show that the incidence of induced abortion increased markedly.((Wm. Robert Johnston, “Historical ​Abortion Statistics, California (USA),​” ​//Abortion statistics and other data-- Johnston`s Archive//, November 21, 2012[[http://​www.johnstonsarchive.net/​policy/​abortion/​usa/​ab-usa-CA.html]]. Accessed ​April 18, 2013).)) Because of the time frame of this study, and because of the eight to 10 years required for the [[biology_of_the_abortion-breast_cancer_link|development of detectable breast cancers]], it is likely that some fraction of the women with detectable cases of breast cancer in this sample had legally procured abortions and some women had illegally procured abortions. (All women were residing in Los Angeles County at the time of their diagnosis, but it may be that some did not live in California at the time of their abortion or procured their abortion elsewhere.) It would have been interesting to assess the timing of the induced abortions alongside corresponding breast cancer diagnoses.
  
-**__Lack of multivariate regressions,​ neglect of potential breast cancer risk factors.__** It is clear that the case and control groups differ significantly across risk factors other than induced abortion. Also, the authors appear not to have conducted multivariate regressions or applied multiple controls to their analysis of induced abortion (or of other risk factors). Some potential breast cancer risk factors appear to have been left out of their analysis. This is likely a consequence of the study’s early date. Lacking multiple controls, this study may attribute the influence of such variables as lower or late parity (or both) or use of oral contraception on breast cancer to induced abortion. Regardless, as we note above, this studylike other such early, developmental,​ suggestive studieswas a step in the development of the field of induced abortion and breast cancer.+**__Lack of multivariate regressions,​ neglect of potential breast cancer risk factors.__** It is clear that the case and control groups differ significantly across risk factors other than induced abortion. Also, the authors appear not to have conducted multivariate regressions or applied multiple controls to their analysis of induced abortion (or of other risk factors). Some potential breast cancer risk factors appear to have been left out of their analysis. This is likely a consequence of the study’s early date. Lacking multiple controls, this study may attribute the influence of such variables as lower or late parity (or both) or use of oral contraception on breast cancer to induced abortion. Regardless, this study---like other such early, developmental,​ suggestive studies---was a step in the development of the field of induced abortion and breast cancer.
  
-**__Pregnancy outcomes.__** The authors found a significant increase in breast cancer risk among women who experience an “early” abortion (i.e., an abortion before 12 weeks’ gestation) prior to their first full-term pregnancy. They do not distinguish between induced and spontaneous abortion; 11 of the 24 abortions among cases and eight of 17 abortions among the controls were induced. Those women who subsequently had a full-term pregnancy saw a somewhat reduced risk of breast cancer, though the authors do not specify how precisely this risk reduction is determinable. The authors also note that abortions after first full-term pregnancy or after three months’ gestation did not appear to increase one’s risk of breast cancer. Pike et al. do not assess the influence of induced abortion history, in general, or the influence of repeated induced abortions or gestational period of or maternal age at induced abortion.+**__Pregnancy outcomes.__** The authors found a significant increase in breast cancer risk among women who experience an “early” abortion (i.e., an abortion before 12 weeks’ gestation) prior to their first full-term pregnancy. They do not distinguish between induced and spontaneous abortion; 11 of the 24 abortions among cases and eight of 17 abortions among the controls were induced. Those women who subsequently had a full-term pregnancy saw a somewhat ​[[effects_of_pregnancy_on_breast_cancer_risks|reduced risk of breast cancer]], though the authors do not specify how precisely this risk reduction is determinable. The authors also note that abortions after first full-term pregnancy or after three months’ gestation did not appear to increase one’s risk of breast cancer. Pike et al. do not assess the influence of induced abortion history, in general, or the influence of repeated induced abortions or gestational period of or maternal age at induced abortion.
  
 **__Full-term pregnancy and age at first full-term pregnancy.__** Ever having a full-term pregnancy and age at first full-term pregnancy (as a trend) were not found to significantly affect the risk of breast cancer. **__Full-term pregnancy and age at first full-term pregnancy.__** Ever having a full-term pregnancy and age at first full-term pregnancy (as a trend) were not found to significantly affect the risk of breast cancer.
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 =====5. 1982 Nishiyama Study===== =====5. 1982 Nishiyama Study=====
  
-Brind notes in his 1996 meta-analysis((Joel Brind, Vernon M. Chinchilli, Walter B. Severs, and Joan Summy-Long, “Induced Abortion as an Independent Risk Factor for Breast Cancer: A Comprehensive Review and Meta-Analysis,​” //Journal of Epidemiology and Community Health// 50, no. 5 (1996): 484.)) that the 1982 Nishiyama study,((F. Nishiyama, “The Epidemiology of Breast Cancer in Tokushima Prefecture,​” //Shikoku Ichi// 38 (1982): 333-343. )) which was written in Japanese, “compared 767 radical mastectomy patients from a single prefecture in Japan with an equal number of age matched, normal controls identified through a mass breast cancer screening programme.” According to Brind’s report, the Nishiyama study showed induced abortion to have a positive, significant influence on breast cancer risk.+Brind notes in his 1996 meta-analysis((Joel Brind, Vernon M. Chinchilli, Walter B. Severs, and Joan Summy-Long, “Induced Abortion as an Independent Risk Factor for Breast Cancer: A Comprehensive Review and Meta-Analysis,​” //Journal of Epidemiology and Community Health// 50, no. 5 (1996): 484.)) that the [[studies_on_the_abortion-breast_cancer_link|1982 Nishiyama study]],((F. Nishiyama, “The Epidemiology of Breast Cancer in Tokushima Prefecture,​” //Shikoku Ichi// 38(1982): 333-343. )) which was written in Japanese, “compared 767 radical mastectomy patients from a single prefecture in Japan with an equal number of age matched, normal controls identified through a mass breast cancer screening programme.” According to Brind’s report, the Nishiyama study showed induced abortion to have a positive, significant influence on breast cancer risk.
  
 =====6. 1988 Ewertz and Duffy Study===== =====6. 1988 Ewertz and Duffy Study=====
  
-In 1988, Ewertz and Duffy((M. Ewertz and S.W. Duffy, “Risk of breast cancer ​in relation ​to reproductive factors ​in Denmark,” //British Journal of Cancer// 58, no. 1 (1988): 99-104.)) found that having one induced abortion contributed to increased risk of breast cancer among Danish women. This study is marked by health and survivor bias, its analyses neglect some breast cancer risk factors and are not multivariate regressions,​ it may be marked by difficulties related to reporting and induced abortion law changes, and in some cases it does not distinguish between induced and spontaneous abortion (e.g., when assessing the influence of breast cancer with respect to the timing of one’s first full-term pregnancy). Regardless, as in the case of the Pike study, Ewertz and Duffy’s study was a step in the development of the field of induced abortion and breast cancer.+In 1988, Ewertz and Duffy((M. Ewertz and S.W. Duffy, “Risk of Breast Cancer ​in Relation ​to Reproductive Factors ​in Denmark,” //British Journal of Cancer// 58, no. 1 (1988): 99-104.)) found that having one induced abortion contributed to increased risk of breast cancer among Danish women. This study is marked by health and survivor bias, its analyses neglect some breast cancer risk factors and are not multivariate regressions,​ it may be marked by difficulties related to reporting and induced abortion law changes, and in some cases it does not distinguish between induced and spontaneous abortion (e.g., when assessing the influence of breast cancer with respect to the timing of one’s first full-term pregnancy). Regardless, as in the case of the Pike study, Ewertz and Duffy’s study was a step in the development of the field of induced abortion and breast cancer.
  
-The authors conducted a study comprised of 1,486 cases and 1,336 controls residing in Denmark. The cases were women under 70 years of age who had been diagnosed with invasive breast cancer or carcinoma in situ between March 1983 and March 1984, who were identified through the Danish Breast Cancer Co-operative Group and the Danish Cancer Registry. Controls were identified through the Danish Central Population Registry.+The authors conducted a study comprised of 1,486 cases and 1,336 controls residing in Denmark. The cases were women under 70 years of age who had been diagnosed with invasive breast cancer or carcinoma in situ between March 1983 and March 1984, and who were identified through the Danish Breast Cancer Co-operative Group and the Danish Cancer Registry. Controls were identified through the Danish Central Population Registry.
  
-**__Health or survivor bias.__** The Ewertz and Duffy study is marked by health and survivor bias. Cases and controls with previous history of breast cancer were excluded.((If the correlation between induced abortion and breast cancer exists, a univariate bias (throwing out controls with a previous history of breast cancer) throws out aborting people (in the control group). Because the control group has even fewer abortions now (in proportion to the levels cases exhibit), the statistic shows an even stronger correlation (more effect) between induced abortion and breast cancer: Throwing out controls with a previous history of breast cancer would bias the effect of induced abortion upward. \\ If there is no correlation between induced abortion and breast cancer, throwing out controls with a previous history of breast cancer would not throw out any extra aborting women (in proportion) in the control group. Aborting women (not being any more likely to have had breast cancer than the other controls) are dropped with the same frequency as the other controls: Throwing out controls with a previous history of breast cancer would not bias the analysis.)) Some cases died, and some were not notified in time to participate in the study, so they were excluded as well. Most women in the Ewertz and Duffy studyaround 90 percent of those who responded to the invitation to participate in the questionnairewere diagnosed after age 40: around one-third were diagnosed in their 40s, around one third were diagnosed in their 50s, and around one-third were diagnosed in their 60s. If breast cancer resulting from an induced abortion is most likely to manifest itself around a decade to 14 years after the abortion’s being procured, then the exclusion of women with a previous history of breast cancer likely eliminated all women whose breast cancer was the result of an induced abortion. These survivor or health biases could have skewed the study’s results away from induced abortion-breast cancer linkage.+**__Health or survivor bias.__** The Ewertz and Duffy study is marked by health and survivor bias. Cases and controls with previous history of breast cancer were excluded.((If the correlation between induced abortion and breast cancer exists, a univariate bias (throwing out controls with a previous history of breast cancer) throws out aborting people (in the control group). Because the control group has even fewer abortions now (in proportion to the levels cases exhibit), the statistic shows an even stronger correlation (more effect) between induced abortion and breast cancer: Throwing out controls with a previous history of breast cancer would bias the effect of induced abortion upward. \\ If there is no correlation between induced abortion and breast cancer, throwing out controls with a previous history of breast cancer would not throw out any extra aborting women (in proportion) in the control group. Aborting women (not being any more likely to have had breast cancer than the other controls) are dropped with the same frequency as the other controls: Throwing out controls with a previous history of breast cancer would not bias the analysis.)) Some cases died, and some were not notified in time to participate in the study, so they were excluded as well. Most women in the Ewertz and Duffy study---around 90 percent of those who responded to the invitation to participate in the questionnaire---were diagnosed after age 40: around one-third were diagnosed in their 40s, around one third were diagnosed in their 50s, and around one-third were diagnosed in their 60s. If breast cancer resulting from an induced abortion is most likely to manifest itself around a decade to 14 years after the abortion’s being procured, then the exclusion of women with a previous history of breast cancer likely eliminated all women whose breast cancer was the result of an induced abortion. These survivor or health biases could have skewed the study’s results away from induced abortion-breast cancer linkage.
  
-**__Reporting difficulty around abortion law change.__** The study also may be marked by difficulties related to abortion law changes. As we note in our analysis of Melbye et al., induced abortion law was liberalized in Denmark in 1973 (around a decade before the breast cancers included in this study were diagnosed). Many women diagnosed with breast cancer in the Ewertz and Duffy study were well past their reproductive years and, hence, past any “need” for induced abortion at the time of its legalization. These women may have procured illegal abortions and may be reluctant to report them for the purposes of the study. Their classification as non-aborting may have skewed the data away from induced abortion-breast cancer linkage.+**__Reporting difficulty around abortion law change.__** The study also may be marked by difficulties related to abortion law changes. As noted in the analysis of Melbye et al., induced abortion law was liberalized in Denmark in 1973 (around a decade before the breast cancers included in this study were diagnosed). Many women diagnosed with breast cancer in the Ewertz and Duffy study were well past their reproductive years and, hence, past any “need” for induced abortion at the time of its legalization. These women may have procured illegal abortions and may be reluctant to report them for the purposes of the study. Their classification as non-aborting may have skewed the data away from induced abortion-breast cancer linkage.
  
-**__Lack of multivariate regressions.__** The authors analyze and control for differences between age at diagnosis, marital status, and residence between cases and controls, but their analyses are not multivariate regressions. Lacking multiple controls, this study may attribute the influence of other variables on breast cancer to induced abortion. Their various analyses include variables for age at menarche, age at natural menopause, menopausal status, whether one’s first pregnancy was incomplete, number of full-term pregnancies,​ age at first full-term pregnancy, type (e.g., spontaneous or induced) and timing of abortion (relative to first full-term pregnancy), type of cancer contracted, and oral contraceptive use.+**__Lack of multivariate regressions.__** The authors analyze and control for differences between age at diagnosis, marital status, and residence between cases and controls, but their analyses are not multivariate regressions. Lacking multiple controls, this study may attribute the influence of other variables on breast cancer to induced abortion. Their various analyses include variables for age at menarche, age at natural menopause, menopausal status, whether one’s first pregnancy was [[effects_of_miscarriage_on_breast_cancer_risks|incomplete]], number of full-term pregnancies,​ age at first full-term pregnancy, type (e.g., spontaneous or induced) and timing of abortion (relative to first full-term pregnancy), type of cancer contracted, and oral contraceptive use.
  
 **__Pregnancy outcomes.__** In their general model, Ewertz and Duffy adjust their risk ratios for age at breast cancer diagnosis and place of residence. Relative to one’s first pregnancy being a full-term pregnancy (by which Ewertz et al. mean a pregnancy lasting 28 weeks or longer), “early termination” of one’s first pregnancy positively and significantly influenced one’s risk of breast cancer. Never experiencing pregnancy also positively and significantly increased one’s risk of breast cancer. **__Pregnancy outcomes.__** In their general model, Ewertz and Duffy adjust their risk ratios for age at breast cancer diagnosis and place of residence. Relative to one’s first pregnancy being a full-term pregnancy (by which Ewertz et al. mean a pregnancy lasting 28 weeks or longer), “early termination” of one’s first pregnancy positively and significantly influenced one’s risk of breast cancer. Never experiencing pregnancy also positively and significantly increased one’s risk of breast cancer.
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 Relative to women with no induced or spontaneous abortions (whose first pregnancy was carried to term), among women with no full-term pregnancies,​ experiencing any type of abortion (spontaneous or induced) was found to increase one’s risk of breast cancer. Relative to women with no induced or spontaneous abortions (whose first pregnancy was carried to term), among women with no full-term pregnancies,​ experiencing any type of abortion (spontaneous or induced) was found to increase one’s risk of breast cancer.
  
-However, no significant effect was found based on the timing of abortion relative to one’s first full-term pregnancy. This may be because, though the authors distinguish abortions as taking place either before or after first full-term pregnancy and based on the trimester in which they take place, they fail to distinguish between spontaneous and induced abortions. ​We assume ​they have chosen not to do so because the resulting categories would be too small for any “signal” to be perceptible above fluctuations (in responses) from other sources of error.+However, no significant effect was found based on the timing of abortion relative to one’s first full-term pregnancy. This may be because, though the authors distinguish abortions as taking place either before or after first full-term pregnancy and based on the trimester in which they take place, they fail to distinguish between spontaneous and induced abortions. ​It has been assumed ​they have chosen not to do so because the resulting categories would be too small for any “signal” to be perceptible above fluctuations (in responses) from other sources of error.
  
 **__Too-simple analysis of abortion.__** Ewertz and Duffy did not assess the influence of maternal age on either general abortion or abortions broken out by type (induced and spontaneous) on breast cancer risk. **__Too-simple analysis of abortion.__** Ewertz and Duffy did not assess the influence of maternal age on either general abortion or abortions broken out by type (induced and spontaneous) on breast cancer risk.
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 **__Induced abortion.__** When stratifying by type of abortion, the authors found that one induced abortion among women with no full-term pregnancies had a positive, significant influence on breast cancer risk, relative to women with no induced or spontaneous abortions (i.e., those women whose first pregnancy was carried to term). That a significant effect was detected is all the more remarkable considering that, compared to 1,142 cases and 1,116 controls with no abortion history, only 13 cases and three controls had induced abortion history. **__Induced abortion.__** When stratifying by type of abortion, the authors found that one induced abortion among women with no full-term pregnancies had a positive, significant influence on breast cancer risk, relative to women with no induced or spontaneous abortions (i.e., those women whose first pregnancy was carried to term). That a significant effect was detected is all the more remarkable considering that, compared to 1,142 cases and 1,116 controls with no abortion history, only 13 cases and three controls had induced abortion history.
  
-**__Spontaneous abortion.__** No significant effect was found for first-trimester spontaneous abortions or for second-trimester spontaneous abortions. Though the latter contradicts ​our hypothesis, it may be merely due to the fact that only three cases and two controls had had a second-trimester spontaneous abortion.+**__Spontaneous abortion.__** No significant effect was found for first-trimester spontaneous abortions or for second-trimester spontaneous abortions. Though the latter contradicts ​the hypothesis, it may be merely due to the fact that only three cases and two controls had had a second-trimester spontaneous abortion.
  
 Ewertz and Duffy chose the correct comparison group for their aborting cohorts— women with no abortions and at least one full-term pregnancy. Ewertz and Duffy chose the correct comparison group for their aborting cohorts— women with no abortions and at least one full-term pregnancy.
  
-**__Number of full-term pregnancies.__** Relative to having only one full-term pregnancy, having four or more full-term pregnancies was significantly protective against breast cancer. (One’s first pregnancy continuing to term, we have already seen, is protective, relative to early termination or never being pregnant. Having four or more full-term pregnancies is not merely protective, relative to nulliparity;​ it is protective relative to having one full-term pregnancy!) As a trend, increasing the number of full-term pregnancies was negatively correlated with breast cancer risk, and this trend was precisely determinable. The authors would have done well to use nulliparity as the reference category in their analysis of the number of full-term pregnancies. As their regression tables are currently designed, the benefits of increasing numbers of full-term pregnancies are less than clear.+**__Number of full-term pregnancies.__** Relative to having only one full-term pregnancy, having four or more full-term pregnancies was significantly ​[[effects_of_pregnancy_on_breast_cancer_risks|protective against breast cancer]]. (One’s first pregnancy continuing to term is protective, relative to early termination or never being pregnant. Having four or more full-term pregnancies is not merely protective, relative to nulliparity;​ it is protective relative to having one full-term pregnancy!) As a trend, increasing the number of full-term pregnancies was negatively correlated with breast cancer risk, and this trend was precisely determinable. The authors would have done well to use nulliparity as the reference category in their analysis of the number of full-term pregnancies. As their regression tables are currently designed, the benefits of increasing numbers of full-term pregnancies are less than clear.
  
 **__Age at first full-term pregnancy.__** No particular age at first pregnancy was found to be significantly protective, and as a trend, age at first pregnancy was not found to have any significant association with breast cancer risk. **__Age at first full-term pregnancy.__** No particular age at first pregnancy was found to be significantly protective, and as a trend, age at first pregnancy was not found to have any significant association with breast cancer risk.
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 **__Age at first full-term pregnancy and age at breast cancer diagnosis.__** The risk associated with increasing age at first full-term pregnancy increased among women diagnosed before age 60 but decreased among those diagnosed after age 60. **__Age at first full-term pregnancy and age at breast cancer diagnosis.__** The risk associated with increasing age at first full-term pregnancy increased among women diagnosed before age 60 but decreased among those diagnosed after age 60.
  
-**__Number of full-term pregnancies,​ age at first full-term pregnancy, and diagnosis with breast cancer before or after age 60.__** The authors tentatively suggest that whereas age at first full-term pregnancy is of more importance than parity among women diagnosed before age 60, parity may be of more importance than age at first full-term pregnancy thereafter. Interpreted:​ One’s age at first full-term pregnancy is determined at least in part by procured abortions and use of contraception. Any effect of these factors can only persist for a decade to 14 years or so after exposure.((Dolle et al. show a positive and significant increase in breast cancer risk in women who used oral contraception one to fewer than five years in the past and 10 to fewer than 15 years in the past. Current oral contraceptive use and use one to fewer than five, five to fewer than 10, and 10 to fewer than 15 years in the past was shown to have a positive and significant influence on triple-negative breast cancer risk. However, for no breast cancer category assessed was any effect was detected for oral contraceptive use 15 or more years in the past. See Jessica M. Dolle, Janet R. Daling, Emily White, Louise A. Brinton, David R. Doody, Peggy L. Porter, and Kathleen E. Malone, “Risk Factors for Triple-Negative Breast Cancer in Women Under the Age of 45 Years,” //Cancer Epidemiology,​ Biomarkers and Prevention//​ 18, no. 4 (2009): 1159. \\ See also [[http://​marri.us/​abortion-breast-cancer|Appendix D]] for further explanation on breast cancer’s manifestation.)) Hence, age at first full-term pregnancy is important in determining breast cancer risk prior to age 60: the effects of abortion and hormonal contraception are unlikely to persist long after the reproductive years have ended and these factors are no longer active. After age 60, these factors are no longer active. The body is susceptible to other environmental factors, and one’s susceptibility is determined by parity (i.e., how much protection has been built up in the body), which is less directly affected by use of oral contraceptives and induced abortion. However, the authors note that “[f]ormal statistical significance was…barely reached in these analyses, so interpretation must be cautious.”+**__Number of full-term pregnancies,​ age at first full-term pregnancy, and diagnosis with breast cancer before or after age 60.__** The authors tentatively suggest that whereas age at first full-term pregnancy is of more importance than parity among women diagnosed before age 60, parity may be of more importance than age at first full-term pregnancy thereafter. Interpreted:​ One’s age at first full-term pregnancy is determined at least in part by procured abortions and use of contraception. Any effect of these factors can only persist for a decade to 14 years or so after exposure.((Dolle et al. show a positive and significant increase in breast cancer risk in women who used oral contraception one to fewer than five years in the past and 10 to fewer than 15 years in the past. Current oral contraceptive use and use one to fewer than five, five to fewer than 10, and 10 to fewer than 15 years in the past was shown to have a positive and significant influence on triple-negative breast cancer risk. However, for no breast cancer category assessed was any effect was detected for oral contraceptive use 15 or more years in the past. See Jessica M. Dolle, Janet R. Daling, Emily White, Louise A. Brinton, David R. Doody, Peggy L. Porter, and Kathleen E. Malone, “Risk Factors for Triple-Negative Breast Cancer in Women Under the Age of 45 Years,” //Cancer Epidemiology,​ Biomarkers and Prevention//​ 18, no. 4 (2009): 1159. \\ See also [[http://​marri.us/​research/​research-papers/​induced-abortion-and-breast-cancer/|Appendix D]] for further explanation on breast cancer’s manifestation.)) Hence, age at first full-term pregnancy is important in determining breast cancer risk prior to age 60: the effects of abortion and hormonal contraception are unlikely to persist long after the reproductive years have ended and these factors are no longer active. After age 60, these factors are no longer active. The body is susceptible to other environmental factors, and one’s susceptibility is determined by parity (i.e., how much protection has been built up in the body), which is less directly affected by use of oral contraceptives and induced abortion. However, the authors note that “[f]ormal statistical significance was…barely reached in these analyses, so interpretation must be cautious.”
  
 **__Age at menarche.__** Ewertz and Duffy find menarche at 15 years of age or 16 years of age or older to be significantly protective against (i.e., to be negatively correlated with) breast cancer, relative to menarche prior to age 13. As a trend, increasing age at menarche was negatively associated with breast cancer risk, and this trend was very precisely determinable. **__Age at menarche.__** Ewertz and Duffy find menarche at 15 years of age or 16 years of age or older to be significantly protective against (i.e., to be negatively correlated with) breast cancer, relative to menarche prior to age 13. As a trend, increasing age at menarche was negatively associated with breast cancer risk, and this trend was very precisely determinable.
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 =====7. 1989 Howe Study===== =====7. 1989 Howe Study=====
  
-Howe et al.((Holly L. Howe, Ruby T. Senie, Helen Bzduch, and Peter Herzfeld, “Early Abortion and Breast Cancer Risk Among Women Under Age 40,” //​International Journal of Epidemiology//​ 18 (1989): 300-304.)) found in 1989 that induced abortions before 20 weeks’ gestation had a positive, significant influence on breast cancer risk. The study is flawed by a lack of data on parity for women who did not experience an induced or spontaneous abortion, short time period between abortion and breast cancer diagnosis, possible reporting difficulties surrounding abortion law change, underreporting and inconsistent distinguishing between induced and spontaneous abortions, a lack of distinction between first- and second-trimester spontaneous abortions, an apparent lack of multiple controls, and a small model. However, the authors restrict their analysis to women under 40 at the time of their diagnosis, an effort that would have protected their analysis to some degree from health or survivor bias, and their model is a record linkage model, eliminating any possibility that the “recall bias” or differential “reporting bias” between cases and controls that some assert undermines case-control studies could taint their work.+Howe et al.((Holly L. Howe, Ruby T. Senie, Helen Bzduch, and Peter Herzfeld, “Early Abortion and Breast Cancer Risk Among Women Under Age 40,” //​International Journal of Epidemiology//​ 18(1989): 300-304.)) found in 1989 that induced abortions before 20 weeks’ gestation had a positive, significant influence on breast cancer risk. The study is flawed by a lack of data on parity for women who did not experience an induced or spontaneous abortion, short time period between abortion and breast cancer diagnosis, possible reporting difficulties surrounding abortion law change, underreporting and inconsistent distinguishing between induced and spontaneous abortions, a lack of distinction between first- and second-trimester spontaneous abortions, an apparent lack of multiple controls, and a small model. However, the authors restrict their analysis to women under 40 at the time of their diagnosis, an effort that would have protected their analysis to some degree from health or survivor bias, and their model is a record linkage model, eliminating any possibility that the “recall bias” or differential “reporting bias” between cases and controls that some assert undermines case-control studies could taint their work.
  
 The authors identified 1,451 women with breast cancer using public records in New York State (excluding women in New York City), which legalized abortion on demand up to 24 weeks in 1970. One control was matched to each case using New York State driver’s license records. All women were matched to public health records on incidence of fetal death, whether a fetal death occurred through spontaneous abortion or induced abortion, between 1971 and 1980. (Fetal deaths after breast cancer diagnosis were not included.) These records also included information on previous pregnancies and their outcomes. The study’s sample was confined to pregnancies lasting 20 weeks or fewer. The authors identified 1,451 women with breast cancer using public records in New York State (excluding women in New York City), which legalized abortion on demand up to 24 weeks in 1970. One control was matched to each case using New York State driver’s license records. All women were matched to public health records on incidence of fetal death, whether a fetal death occurred through spontaneous abortion or induced abortion, between 1971 and 1980. (Fetal deaths after breast cancer diagnosis were not included.) These records also included information on previous pregnancies and their outcomes. The study’s sample was confined to pregnancies lasting 20 weeks or fewer.
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 =====8. 1993 Laing Study===== =====8. 1993 Laing Study=====
  
-Laing et al.’s study of breast cancer in African-American women in Washington, D.C., was released in 1993.((A.E. Laing, Florence M. Demenais, Rosemary Williams, Grace Kissling, Vivien W. Chen, and George Bonney,” Breast Cancer Risk Factors In African-American Women: The Howard University Tumor Registry Experience,” //Journal of the National Medical Association//​ 85 (1993): 931-939.)) The study cited a need for specific research into breast cancer in black women because of an uptick in breast cancer incidence among under-40 black women and an increase in breast cancer mortality among black women younger than 50. The study found induced abortion had a positive, significant influence on breast cancer risk among women diagnosed at age 50 or older and a positive, marginally significant influence among women diagnosed between the ages of 41 and 49. This study is of limited generalizability (because of its exclusion to African-American women), is marked by health bias, excludes important data on various important breast cancer risk factors (and thereby risks introducing omitted variable bias), contains possible reporting difficulties surrounding abortion law changes, fails to distinguish between first- and second-trimester spontaneous abortions, and conducts an unsophisticated analysis of induced abortions.+Laing et al.’s study of breast cancer in African-American women in Washington, D.C., was released in 1993.((A.E. Laing, Florence M. Demenais, Rosemary Williams, Grace Kissling, Vivien W. Chen, and George Bonney, ​"Breast Cancer Risk Factors In African-American Women: The Howard University Tumor Registry Experience," ​//Journal of the National Medical Association//​ 85(1993): 931-939.)) The study cited a need for specific research into breast cancer in black women because of an uptick in breast cancer incidence among under-40 black women and an increase in breast cancer mortality among black women younger than 50. The study found induced abortion had a positive, significant influence on breast cancer risk among women diagnosed at age 50 or older and a positive, marginally significant influence among women diagnosed between the ages of 41 and 49. This study is of limited generalizability (because of its exclusion to African-American women), is marked by health bias, excludes important data on various important breast cancer risk factors (and thereby risks introducing omitted variable bias), contains possible reporting difficulties surrounding abortion law changes, fails to distinguish between first- and second-trimester spontaneous abortions, and conducts an unsophisticated analysis of induced abortions.
  
 **__Limited generalizability,​ health or survivor bias.__** The study included 503 African-American cases identified through Howard University Hospital in Washington, D.C., between 1978 and 1987. Five hundred thirty-nine African-American age-matched controls who presented with “nonmalignant conditions” at the same hospital were also included in the study. This restriction of the study to African-American women limits its generalizability,​ and the exclusion of controls with breast cancer is a health bias that could skew the results of their analysis away from linkage between induced abortion and breast cancer. **__Limited generalizability,​ health or survivor bias.__** The study included 503 African-American cases identified through Howard University Hospital in Washington, D.C., between 1978 and 1987. Five hundred thirty-nine African-American age-matched controls who presented with “nonmalignant conditions” at the same hospital were also included in the study. This restriction of the study to African-American women limits its generalizability,​ and the exclusion of controls with breast cancer is a health bias that could skew the results of their analysis away from linkage between induced abortion and breast cancer.
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 Laing et al. note evidence of possible underreporting among older controls, which may have shifted the odds ratio associated with breast cancer and abortion upward. The authors state that whereas consistent numbers of cases report induced abortions across age at diagnosis categories, fewer induced abortions are reported by older controls. They find no such shift in spontaneous abortion incidence. Laing et al. note evidence of possible underreporting among older controls, which may have shifted the odds ratio associated with breast cancer and abortion upward. The authors state that whereas consistent numbers of cases report induced abortions across age at diagnosis categories, fewer induced abortions are reported by older controls. They find no such shift in spontaneous abortion incidence.
  
-The assertion Laing et al. make is unnecessary for explaining the pattern they see in their data. It is clear that many more cases than controls reported induced abortions in the cohort of women fifty and older at their breast cancer diagnosis. However, these cases were diagnosed five to 14 years after Roe v. Wade, meaning the youngest of the women in this cohort were 36. There would be less demand for abortion in a group so late into their reproductive years. (In 1996, only 10 percent of all abortions in the U.S. were procured by women age 35 or older; this proportion had changed little by 2000 and 2008, in which years about 11 percent of all abortions in the U.S. were procured by women aged 35 or older.((Gilda Sedgh, Akinrinola Bankole, Susheela Singh, and Michelle Eilers, “Legal Abortion Levels and Trends By Woman’s Age at Termination,​” International Perspectives on Sexual and Reproductive Health 38, no. 3 (September 2012): 144. [[http://​www.guttmacher.org/​pubs/​journals/​3814312.pdf]] ​(accessed ​July 5, 2013).))) A smaller fraction of women in this cohort took “advantage” of the change legalizing induced abortion. Additionally,​ women who do choose to procure abortions at this age may be at greater risk of breast cancer than women who procure abortions slightly earlier in their reproductive lives. Thus, there is no need for the hypothesis of reporting bias as it is put forward, but in no way analyzed, by the authors.+The assertion Laing et al. make is unnecessary for explaining the pattern they see in their data. It is clear that many more cases than controls reported induced abortions in the cohort of women fifty and older at their breast cancer diagnosis. However, these cases were diagnosed five to 14 years after Roe v. Wade, meaning the youngest of the women in this cohort were 36. There would be less demand for abortion in a group so late into their reproductive years. (In 1996, only 10 percent of all abortions in the U.S. were procured by women age 35 or older; this proportion had changed little by 2000 and 2008, in which years about 11 percent of all abortions in the U.S. were procured by women aged 35 or older.((Gilda Sedgh, Akinrinola Bankole, Susheela Singh, and Michelle Eilers, “Legal Abortion Levels and Trends By Woman’s Age at Termination,​” ​//International Perspectives on Sexual and Reproductive Health// 38, no. 3 (September 2012): 144. Available at [[http://​www.guttmacher.org/​pubs/​journals/​3814312.pdf]]. Accessed ​July 5, 2013.))) A smaller fraction of women in this cohort took “advantage” of the change legalizing induced abortion. Additionally,​ women who do choose to procure abortions at this age may be at greater risk of breast cancer than women who procure abortions slightly earlier in their reproductive lives. Thus, there is no need for the hypothesis of reporting bias as it is put forward, but in no way analyzed, by the authors.
  
 **__Unsophisticated analysis of induced abortion.__** The authors do not assess the differing effects of induced abortion based on the gestational period at which it was procured, on maternal age at first induced abortion, or on number of induced abortions procured. Though the authors control for parity, they do not assess the effects of induced abortion’s timing relative to first full-term pregnancy, and hence do not examine the effect of parity status at the time of one’s induced abortion on one’s vulnerability. **__Unsophisticated analysis of induced abortion.__** The authors do not assess the differing effects of induced abortion based on the gestational period at which it was procured, on maternal age at first induced abortion, or on number of induced abortions procured. Though the authors control for parity, they do not assess the effects of induced abortion’s timing relative to first full-term pregnancy, and hence do not examine the effect of parity status at the time of one’s induced abortion on one’s vulnerability.
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 =====9. 1994 Daling Study===== =====9. 1994 Daling Study=====
  
-Public attention was drawn to the induced abortion-breast cancer link in 1994, when TIME magazine covered((Christine Gorman, “Do Abortions Raise the Risk of Breast Cancer?” //TIME//, November 7, 1994, 61.)) a U.S. study by Janet Daling commissioned by the National Cancer Institute (NCI).((Janet R. Daling, Kathleen E. Malone, Lynda F. Voigt, Emily White, and Noel S. Weiss, “Risk of Breast Cancer among Young Women: Relationship to Induced Abortions,​” //Journal of the National Cancer Institute// 86 (1994): 1584-1592.)) Daling found that having any induced abortion history significantly increased one’s breast cancer risk. The study is of limited generalizability and is marked by possible difficulties related to reporting around abortion law changes, as well as health or survivor bias, but it devotes considerable attention to assessing the risk incurred with induced abortion under different circumstances.+Public attention was drawn to the induced abortion-breast cancer link in 1994, when TIME magazine covered((Christine Gorman, “Do Abortions Raise the Risk of Breast Cancer?” //TIME//, November 7, 1994, 61.)) a U.S. study by Janet Daling commissioned by the National Cancer Institute (NCI).((Janet R. Daling, Kathleen E. Malone, Lynda F. Voigt, Emily White, and Noel S. Weiss, “Risk of Breast Cancer among Young Women: Relationship to Induced Abortions,​” //Journal of the National Cancer Institute// 86(1994): 1584-1592.)) Daling found that having any induced abortion history significantly increased one’s breast cancer risk. The study is of limited generalizability and is marked by possible difficulties related to reporting around abortion law changes, as well as health or survivor bias, but it devotes considerable attention to assessing the risk incurred with induced abortion under different circumstances.
  
 The study’s cases included white women born after 1944 and residing in King, Pierce, and Snohomish counties, Washington, who were diagnosed with invasive or in situ breast cancer between January 1983 and April 1990. The patients were identified through a SEER cancer registry in Washington State. The authors acquired a total sample of 845 cases and 961 controls. Controls were identified through random-digit dialing in King, Pierce, and Snohomish counties. ​ The study’s cases included white women born after 1944 and residing in King, Pierce, and Snohomish counties, Washington, who were diagnosed with invasive or in situ breast cancer between January 1983 and April 1990. The patients were identified through a SEER cancer registry in Washington State. The authors acquired a total sample of 845 cases and 961 controls. Controls were identified through random-digit dialing in King, Pierce, and Snohomish counties. ​
  
-**__Limited generalizability,​ survivor or health bias.__** That all participants were white would limit the generalizability of the study’s findings. The study was confined to women experiencing a first diagnosis of breast cancer; this health or survivor bias could have reduced the strength of the induced abortion-breast cancer link, as we explain ​above. The authors note that a health or survivor bias may have affected their data, because women with induced or spontaneous abortions at a young age who have breast cancer may tend to have a “poor prognosis (16), it could be that those women with breast cancer whom we were unable to interview because of serious illness or death may have been more likely to have had an induced abortion that the women we did interview. If this bias were present, we would have underestimated the risk of breast cancer that is associated with induced abortion.”((Janet R. Daling, Kathleen E. Malone, Lynda F. Voigt, Emily White, and Noel S. Weiss, “Risk of Breast Cancer among Young Women: Relationship to Induced Abortions,​” //Journal of the National Cancer Institute// 86 (1994): 1589.))+**__Limited generalizability,​ survivor or health bias.__** That all participants were white would limit the generalizability of the study’s findings. The study was confined to women experiencing a first diagnosis of breast cancer; this health or survivor bias could have reduced the strength of the induced abortion-breast cancer link, as explained ​above. The authors note that a health or survivor bias may have affected their data, because women with induced or spontaneous abortions at a young age who have breast cancer may tend to have a “poor prognosis (16), it could be that those women with breast cancer whom we were unable to interview because of serious illness or death may have been more likely to have had an induced abortion that the women we did interview. If this bias were present, we would have underestimated the risk of breast cancer that is associated with induced abortion.”((Janet R. Daling, Kathleen E. Malone, Lynda F. Voigt, Emily White, and Noel S. Weiss, “Risk of Breast Cancer among Young Women: Relationship to Induced Abortions,​” //Journal of the National Cancer Institute// 86(1994): 1589.))
  
-**__Reporting difficulty around abortion law change.__** Some of the reproductive years of some fraction of the women studied would have taken place prior to abortion’s 1970 legalization in Washington State,​((National Abortion Federation, “History of Abortion.” [[http://​www.prochoice.org/​about_abortion/​history_abortion.html]] ​(accessed ​April 19, 2013).)) but as the authors note, the study is comprised of “women in whom most or all of their reproductive years occurred after 1970,” and most of the abortions included took place following its legalization.+**__Reporting difficulty around abortion law change.__** Some of the reproductive years of some fraction of the women studied would have taken place prior to abortion’s 1970 legalization in Washington State,​((National Abortion Federation, “History of Abortion.” ​Available at [[http://​www.prochoice.org/​about_abortion/​history_abortion.html]]. Accessed ​April 19, 2013.)) but as the authors note, the study is comprised of “women in whom most or all of their reproductive years occurred after 1970,” and most of the abortions included took place following its legalization.
  
 In addition to containing a large sample, the study’s strength is that its “primary focus…was on the difference in the subsequent risk of breast cancer between pregnant women who did and did not choose to terminate that pregnancy but who, based on their demographic characteristics and childbearing histories, were otherwise at similar risk.” Hence, in analyzing the risk of induced abortion, the authors control for a variety of other factors, such as age, family history of breast cancer, and age at first birth. (Daling et al. even control for religion in their analyses for induced abortion and so attempt to control for any effect of “reporting bias” on the part of devout women.) In addition to containing a large sample, the study’s strength is that its “primary focus…was on the difference in the subsequent risk of breast cancer between pregnant women who did and did not choose to terminate that pregnancy but who, based on their demographic characteristics and childbearing histories, were otherwise at similar risk.” Hence, in analyzing the risk of induced abortion, the authors control for a variety of other factors, such as age, family history of breast cancer, and age at first birth. (Daling et al. even control for religion in their analyses for induced abortion and so attempt to control for any effect of “reporting bias” on the part of devout women.)
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 =====10. 1995 Lipworth Study===== =====10. 1995 Lipworth Study=====
  
-A study of abortion in Greece((Loren Lipworth, Klea Katsouyanni,​ Anders Ekbom, Karin B. Michels, and Dimitrios Trichopoulos,​ “Abortion and the Risk of Breast Cancer: A Case-Control Study in Greece,” //​International Journal of Cancer// 61 (1995): 181-184)) found induced abortion to have a positive, significant influence on breast cancer risk. The study is marked by health or survivor bias and failure to distinguish between first- and second-trimester spontaneous abortions, but it has the benefit of being conducted in a clinical environment,​ which would discourage underreporting.+A study of abortion in Greece((Loren Lipworth, Klea Katsouyanni,​ Anders Ekbom, Karin B. Michels, and Dimitrios Trichopoulos,​ “Abortion and the Risk of Breast Cancer: A Case-Control Study in Greece,” //​International Journal of Cancer// 61(1995): 181-184)) found induced abortion to have a positive, significant influence on breast cancer risk. The study is marked by health or survivor bias and failure to distinguish between first- and second-trimester spontaneous abortions, but it has the benefit of being conducted in a clinical environment,​ which would discourage underreporting.
  
 The Lipworth study contained 820 cases diagnosed with breast cancer between January 1989 and December 1991 in hospitals around Athens. The study also included two matched control groups, comprised of 795 female orthopedic patients and 753 hospital visitors. The Lipworth study contained 820 cases diagnosed with breast cancer between January 1989 and December 1991 in hospitals around Athens. The study also included two matched control groups, comprised of 795 female orthopedic patients and 753 hospital visitors.
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 =====11. 1995 Bu Study (abstract)===== =====11. 1995 Bu Study (abstract)=====
  
-A study of women in Harbin, China,((L. Bu, L.F. Voigt, Z. Yu, K.E. Malone, and J.R. Daling, “Risk of breast cancer associated ​with induced abortion ​in a population ​at low risk of breast cancer,” //American Journal of Epidemiology//​ 141 (1995): S85 (abstract 337).)) found a statistically significantly increased risk of breast cancer among women 45 and younger who had had one induced abortion or two or more induced abortions. This increase in risk was greater when the analysis was confined to women younger than 35. The brief abstract makes no mention of the inclusion of several breast cancer risk factors in its model, its results are generalizable only to parous women, and the mode of its relatively simple analysis of a fairly small sample is unclear, but the study’s confinement to young women could diminish the effects of any health or survivor bias introduced by its “rearward-looking” analysis.+A study of women in Harbin, China,((L. Bu, L.F. Voigt, Z. Yu, K.E. Malone, and J.R. Daling, “Risk of Breast Cancer Associated ​with Induced Abortion ​in a Population ​at Low Risk of Breast Cancer,” //American Journal of Epidemiology//​ 141(1995): S85 (abstract 337).)) found a statistically significantly increased risk of breast cancer among women 45 and younger who had had one induced abortion or two or more induced abortions. This increase in risk was greater when the analysis was confined to women younger than 35. The brief abstract makes no mention of the inclusion of several breast cancer risk factors in its model, its results are generalizable only to parous women, and the mode of its relatively simple analysis of a fairly small sample is unclear, but the study’s confinement to young women could diminish the effects of any health or survivor bias introduced by its “rearward-looking” analysis.
  
 **__Small sample, limited generalizability.__** The study was confined to parous women younger than 45 at the time of their diagnosis with breast cancer. Its confinement to parous women limits its generalizability. The 232 cases were diagnosed between October 1990 and December 1992. Each case was matched for age and neighborhood with two controls. Their sample is thus relatively small. Information was obtained regarding the reproductive history of cases and controls. **__Small sample, limited generalizability.__** The study was confined to parous women younger than 45 at the time of their diagnosis with breast cancer. Its confinement to parous women limits its generalizability. The 232 cases were diagnosed between October 1990 and December 1992. Each case was matched for age and neighborhood with two controls. Their sample is thus relatively small. Information was obtained regarding the reproductive history of cases and controls.
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 =====13. 1999 Fioretti Study===== =====13. 1999 Fioretti Study=====
  
-An Italian study((F. Fioretti, A. Tavani, C. Bosetti, C. La Vecchia, E. Negri, F. Barbone, R. Talamini, and S. Franceschi, “Risk ​factors ​for breast cancer ​in nulliparous women,” //British Journal of Cancer// 78, no. 11/12 (1999): 1923-1928.)) comprised of data from the 1987 and 1995 La Vecchia studies showed a risk of breast cancer among nulliparous women having abortions late in their reproductive lives. The study is of limited generalizability due to its restriction to nulliparous women, is marked by health bias, does not distinguish between first- and second-trimester spontaneous abortions, does not apply multiple controls uniformly across its analyses, and in its more sophisticated analyses (e.g., age at first abortion) fails to distinguish between induced and spontaneous abortions.+An Italian study((F. Fioretti, A. Tavani, C. Bosetti, C. La Vecchia, E. Negri, F. Barbone, R. Talamini, and S. Franceschi, “Risk ​Factors ​for Breast Cancer ​in Nulliparous Women,” //British Journal of Cancer// 78, no. 11/12 (1999): 1923-1928.)) comprised of data from the 1987 and 1995 La Vecchia studies showed a risk of breast cancer among nulliparous women having abortions late in their reproductive lives. The study is of limited generalizability due to its restriction to nulliparous women, is marked by health bias, does not distinguish between first- and second-trimester spontaneous abortions, does not apply multiple controls uniformly across its analyses, and in its more sophisticated analyses (e.g., age at first abortion) fails to distinguish between induced and spontaneous abortions.
  
 Fioretti et al. conducted a study deliberately designed to evaluate breast cancer risk among nulliparous women, whom they acknowledge are at increased risk of breast cancer. The study was comprised of 1,041 nulliparous cases between the ages of 22 and 79 and 1,002 nulliparous controls aged 15 to 79 living in six different geographic areas in Italy. Fioretti et al. conducted a study deliberately designed to evaluate breast cancer risk among nulliparous women, whom they acknowledge are at increased risk of breast cancer. The study was comprised of 1,041 nulliparous cases between the ages of 22 and 79 and 1,002 nulliparous controls aged 15 to 79 living in six different geographic areas in Italy.
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 These alterations drew a reaction from some members of the U.S. Congress, which has budgetary and political oversight of the NCI. That year, 28 congressmen signed a letter asking the NCI to amend its website concerning the link between breast cancer and induced abortion, as a large quantity of the data demonstrated a risk. These alterations drew a reaction from some members of the U.S. Congress, which has budgetary and political oversight of the NCI. That year, 28 congressmen signed a letter asking the NCI to amend its website concerning the link between breast cancer and induced abortion, as a large quantity of the data demonstrated a risk.
  
-The letter resulted in the removal of this page from the website, pending a February 2003 workshop on “Early Reproductive Events and Breast Cancer Risk” conducted by the NCI. One hundred scientists and breast cancer advocates participated in this three-day workshop; save for one dissenter—Joel Brind—they concluded that induced abortion was not a risk and did not merit further study. The workshop did note, however, that premature delivery was considered an “epidemiologic gap” requiring more study.((National Institutes of Health, National Cancer Institute, ​Summary Report: Early Reproductive Events and Breast Cancer Workshop,” National Cancer Institute [[http://​www.cancer.gov/​cancertopics/​causes/​ere/​workshop-report/​]] ​(accessed ​January 3, 2013).))+The letter resulted in the removal of this page from the website, pending a February 2003 workshop on “Early Reproductive Events and Breast Cancer Risk” conducted by the NCI. One hundred scientists and breast cancer advocates participated in this three-day workshop; save for one dissenter—Joel Brind—they concluded that induced abortion was not a risk and did not merit further study. The workshop did note, however, that premature delivery was considered an “epidemiologic gap” requiring more study.((National Institutes of Health, National Cancer Institute, ​//Summary Report: Early Reproductive Events and Breast Cancer Workshop//, National Cancer Institute. Available at [[http://​www.cancer.gov/​cancertopics/​causes/​ere/​workshop-report/​]]. Accessed ​January 3, 2013.))
  
 =====15. 2003 Becher Study===== =====15. 2003 Becher Study=====
  
-A 2003 study((H. Becher, S. Schmidt, and J. Chang-Claude,​ “Reproductive ​factors ​and familial predisposition ​for breast cancer ​by age 50 years. A case-control-family ​study for assessing main effects ​and possible gene-environment ​interaction,” //​International Journal of Epidemiology//​ 32 (2003): 38-50.)) in Germany designed to assess the importance of reproductive breast cancer risk factors among women genetically susceptible to breast cancer (the authors tested for a “gene-environment interaction”) found an increased risk of breast cancer with induced abortion. The Becher study, while marked (like many studies) by some degree of health or survivor bias, reporting no data on spontaneous abortion, and containing only a simple analysis of induced abortion (it does not, for example, examine the effects of repeated induced abortions), is uniquely beneficial to the field in that it is focused on women genetically predisposed to breast cancer.+A 2003 study((H. Becher, S. Schmidt, and J. Chang-Claude,​ “Reproductive ​Factors ​and Familial Predisposition ​for Breast Cancer ​by Age 50 Years. A Case-Control-family ​Study for Assessing Main Effects ​and Possible Gene-environment ​Interaction,” //​International Journal of Epidemiology//​ 32(2003): 38-50.)) in Germany designed to assess the importance of reproductive breast cancer risk factors among women genetically susceptible to breast cancer (the authors tested for a “gene-environment interaction”) found an increased risk of breast cancer with induced abortion. The Becher study, while marked (like many studies) by some degree of health or survivor bias, reporting no data on spontaneous abortion, and containing only a simple analysis of induced abortion (it does not, for example, examine the effects of repeated induced abortions), is uniquely beneficial to the field in that it is focused on women genetically predisposed to breast cancer.
  
 The study included 706 cases diagnosed with //in situ// or invasive breast cancer in 40 hospitals in two regions in Baden-Württemberg,​ Germany. The women were mainly premenopausal and age 50 or younger at the time of their diagnosis between January 1992 and December 1995. The study also included two sets of controls: 252 sisters of cases and 1,381 age- and region-matched population controls identified through German population registries. The study included 706 cases diagnosed with //in situ// or invasive breast cancer in 40 hospitals in two regions in Baden-Württemberg,​ Germany. The women were mainly premenopausal and age 50 or younger at the time of their diagnosis between January 1992 and December 1995. The study also included two sets of controls: 252 sisters of cases and 1,381 age- and region-matched population controls identified through German population registries.
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 =====16. 2006 Tehranian Presentation (abstract)===== =====16. 2006 Tehranian Presentation (abstract)=====
  
-A 2006 Iranian study found a statistically significant increased risk of breast cancer with induced abortion and with spontaneous abortions after 12 weeks’ gestation.((Najmeh Tehranian, M. Amelbaraez, R. Salke, and S. Faghihzadeh,​ “The ​effect ​of abortion ​on the risk of breast cancer” (Iranian study presented at a conference at McMaster University, 2006). [[http://​www.nursinglibrary.org/​vhl/​handle/​10755/​163877]] ​(accessed ​April 29, 2013). Please note that only the abstract of this study is currently available.)) The brief abstract makes no mention of the inclusion of several breast cancer risk factors in its model, the mode of its relatively simple analysis of a fairly small sample is unclear, and it may be marked by health bias.+A 2006 Iranian study found a statistically significant increased risk of breast cancer with induced abortion and with spontaneous abortions after 12 weeks’ gestation.((Najmeh Tehranian, M. Amelbaraez, R. Salke, and S. Faghihzadeh,​ “The ​Effect ​of Abortion ​on the Risk of Breast Cancer” (Iranian study presented at a conference at McMaster University, 2006). ​Available at [[http://​www.nursinglibrary.org/​vhl/​handle/​10755/​163877]]. Accessed ​April 29, 2013. Please note that only the abstract of this study is currently available.)) The brief abstract makes no mention of the inclusion of several breast cancer risk factors in its model, the mode of its relatively simple analysis of a fairly small sample is unclear, and it may be marked by health bias.
  
 The study included 231 cases and 254 population controls and was conducted at a medical university in Mashhad in 2004. Cases and controls were matched “by age, menstruation,​ family history of breast cancer, breastfeeding,​ duration of oral contraceptive use, history of [“hormone replacement therapy,​”] and body mass index.” The study included 231 cases and 254 population controls and was conducted at a medical university in Mashhad in 2004. Cases and controls were matched “by age, menstruation,​ family history of breast cancer, breastfeeding,​ duration of oral contraceptive use, history of [“hormone replacement therapy,​”] and body mass index.”
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 **__Health or survivor bias.__** It seems that women with breast cancer may have been excluded as controls, who are described as “general healthy population controls,​” a health bias which could introduce error into their analyses and skew their results away from induced abortion-breast cancer linkage. **__Health or survivor bias.__** It seems that women with breast cancer may have been excluded as controls, who are described as “general healthy population controls,​” a health bias which could introduce error into their analyses and skew their results away from induced abortion-breast cancer linkage.
  
-**__Induced abortion.__** Tehranian et al. report that women who had induced abortions prior to 12 weeks’ gestation had a significantly larger breast cancer risk than women who had no induced abortion history.((While some authors might attribute the size of the (substantial) effects conferred by induced abortion in the 2006 Tehranian study, by university education in the 2007 Naieni study, and by induced abortion in the 2011 Khachatryan study, to recall bias, we wonder ​whether the size of the effects is not a consequence of fewer carcinogenic channels in these societies. For example, Khachatryan et al. note that Armenians consume very little alcohol and that very few Armenian women have ever used “hormone replacement therapy” or oral contraception. This reduced exposure to carcinogens would statistically “clarify” any effect of induced abortion (or of any other relevant factor).))+**__Induced abortion.__** Tehranian et al. report that women who had induced abortions prior to 12 weeks’ gestation had a significantly larger breast cancer risk than women who had no induced abortion history.((While some authors might attribute the size of the (substantial) effects conferred by induced abortion in the 2006 Tehranian study, by university education in the 2007 Naieni study, and by induced abortion in the 2011 Khachatryan study, to recall bias, it can be wondered ​whether the size of the effects is not a consequence of fewer carcinogenic channels in these societies. For example, Khachatryan et al. note that Armenians consume very little alcohol and that very few Armenian women have ever used “hormone replacement therapy” or oral contraception. This reduced exposure to carcinogens would statistically “clarify” any effect of induced abortion (or of any other relevant factor).))
  
 **__Too-simple analysis of induced abortion.__** The authors seem not to have assessed induced abortion relative to the timing of first full-term pregnancy, maternal age at the time of induced abortion, or the number of induced abortions. **__Too-simple analysis of induced abortion.__** The authors seem not to have assessed induced abortion relative to the timing of first full-term pregnancy, maternal age at the time of induced abortion, or the number of induced abortions.
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 =====17. 2007 Naieni Study===== =====17. 2007 Naieni Study=====
  
-A 2007 study conducted in the province of Mazandaran in Iran showed a statistically significant increased risk of breast cancer with abortion.((Kourosh Holakouie Naieni, Ali Ardalan, Mahmood Mahmoodi, Abbas Motevalian, Yoosef Yahyapoor, and Bahareh Yazdizadeh, “Risk Factors of Breast Cancer in North of Iran: A Case-Control in Mazandaran Province,​” //Asian Pacific Journal of Cancer Prevention//​ 8 (2007): 395-398. ​[[http://​www.apocp.org/​cancer_download/​Volume8_No3/​395-398%20c_Naieni%204.pdf]] (accessed ​December 7, 2012).)) This study may be skewed by health or survivor bias, conducts only an unsophisticated analysis of induced abortion, and does not distinguish between first- and second-trimester spontaneous abortions.+A 2007 study conducted in the province of Mazandaran in Iran showed a statistically significant increased risk of breast cancer with abortion.((Kourosh Holakouie Naieni, Ali Ardalan, Mahmood Mahmoodi, Abbas Motevalian, Yoosef Yahyapoor, and Bahareh Yazdizadeh, “Risk Factors of Breast Cancer in North of Iran: A Case-Control in Mazandaran Province,​” //Asian Pacific Journal of Cancer Prevention//​ 8(2007): 395-398. ​Accessed ​December 7, 2012.)) This study may be skewed by health or survivor bias, conducts only an unsophisticated analysis of induced abortion, and does not distinguish between first- and second-trimester spontaneous abortions.
  
 The Naieni study included 250 cases aged 22 to 80 chosen through the cancer registry of Babol Research Station, as well as 500 neighborhood-matched controls aged 19 to 77. The authors demonstrate the differences between their cases and controls. In addition to analyzing the effects of induced and spontaneous abortion, the authors implemented a wide variety of controls, such as first-degree family history of breast cancer, personal history of benign breast disease, oral contraceptive use, age at menarche, and menopausal status, as well as factors such as education and household income. The Naieni study included 250 cases aged 22 to 80 chosen through the cancer registry of Babol Research Station, as well as 500 neighborhood-matched controls aged 19 to 77. The authors demonstrate the differences between their cases and controls. In addition to analyzing the effects of induced and spontaneous abortion, the authors implemented a wide variety of controls, such as first-degree family history of breast cancer, personal history of benign breast disease, oral contraceptive use, age at menarche, and menopausal status, as well as factors such as education and household income.
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 =====20. 2009 Ozmen Study===== =====20. 2009 Ozmen Study=====
  
-In 2009, a study in Turkey found induced abortion history contributed to a statistically significant increase in breast cancer risk.((Vahit Ozmen, Beyza Ozcinar, Hasan Karanlik, Neslihan Cabioglu, Mustafa Tukenmez, Rian Disci, Tolga Ozmen, Abdullah Igci, Mahmut Muslumanoglu,​ Mustafa Kecer, and Atilla Soran, “Breast Cancer Risk Factors in Turkish Women– a University Hospital Based Nested Case Control Study,” //World Journal of Surgical Oncology// 7, no. 37 (2009). [[http://​www.wjso.com/​content/​pdf/​1477-7819-7-37.pdf]] ​(accessed ​January 16, 2013).)) The study is marked by health bias, conducts only an unsophisticated analysis of induced abortion, and does not distinguish between first- and second-trimester spontaneous abortions.+In 2009, a study in Turkey found induced abortion history contributed to a statistically significant increase in breast cancer risk.((Vahit Ozmen, Beyza Ozcinar, Hasan Karanlik, Neslihan Cabioglu, Mustafa Tukenmez, Rian Disci, Tolga Ozmen, Abdullah Igci, Mahmut Muslumanoglu,​ Mustafa Kecer, and Atilla Soran, “Breast Cancer Risk Factors in Turkish Women– a University Hospital Based Nested Case Control Study,” //World Journal of Surgical Oncology// 7, no. 37 (2009). ​Available at [[http://​www.wjso.com/​content/​pdf/​1477-7819-7-37.pdf]]. Accessed ​January 16, 2013.)) The study is marked by health bias, conducts only an unsophisticated analysis of induced abortion, and does not distinguish between first- and second-trimester spontaneous abortions.
  
 The Ozmen study was comprised of 1,492 breast cancer patients and 2,167 controls aged 18 to 70 visiting Istanbul University Medical Faculty hospital. (Some patients were also selected from the authors’ breast cancer database.) The authors built a moderately thorough model and specified the differences between cases and controls. Alcohol consumption was consciously excluded from statistical analysis because of the very limited alcohol intake among Turkish women. The Ozmen study was comprised of 1,492 breast cancer patients and 2,167 controls aged 18 to 70 visiting Istanbul University Medical Faculty hospital. (Some patients were also selected from the authors’ breast cancer database.) The authors built a moderately thorough model and specified the differences between cases and controls. Alcohol consumption was consciously excluded from statistical analysis because of the very limited alcohol intake among Turkish women.
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 =====21. 2011 Khachatryan Study===== =====21. 2011 Khachatryan Study=====
  
-In 2011, an Armenian study of the relationship between breast cancer and diabetes mellitus type two by Khachatryan and colleagues showed an increased risk of breast cancer with induced abortion.((L. Khachatryan,​ R. Scharpf, S. Kagan, “Influence of diabetes mellitus type 2 and prolonged estrogen exposure ​on risk of breast cancer ​among women in Armenia,” //Health Care for Women International//​ 32, no. 11 (2011): 953-971.)) The study is marked by health bias, was conducted over the telephone (which could generate underreporting),​ and conducts only a simple analysis of induced abortion with its small sample.+In 2011, an Armenian study of the relationship between breast cancer and diabetes mellitus type two by Khachatryan and colleagues showed an increased risk of breast cancer with induced abortion.((L. Khachatryan,​ R. Scharpf, S. Kagan, “Influence of Diabetes Mellitus Type 2 and Prolonged Estrogen Exposure ​on Risk of Breast Cancer ​among Women in Armenia,” //Health Care for Women International//​ 32, no. 11 (2011): 953-971.)) The study is marked by health bias, was conducted over the telephone (which could generate underreporting),​ and conducts only a simple analysis of induced abortion with its small sample.
  
 The Khachatryan study included 150 cases registered through the National Oncology Center and the Armenian-American Wellness Center between January 2002 and December 2008, as well as 152 controls with no prior history of breast diseases or (non-cosmetic) breast surgeries identified through random digit dialing. The sample was comprised of women aged 35 to 70, residing in Yerevan, Armenia, and participants were interviewed over the telephone. The Khachatryan study included 150 cases registered through the National Oncology Center and the Armenian-American Wellness Center between January 2002 and December 2008, as well as 152 controls with no prior history of breast diseases or (non-cosmetic) breast surgeries identified through random digit dialing. The sample was comprised of women aged 35 to 70, residing in Yerevan, Armenia, and participants were interviewed over the telephone.
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 =====22. 2012 Jiang Study===== =====22. 2012 Jiang Study=====
  
-A 2012 Chinese study of abortion and breast cancer risk((A.R. Jiang, C.M. Gao, J.H. Ding, S.P. Li, Y.T. Liu, H.X. Cao, J.Z. Wu, J.H. Tang, Y. Qian, and K. Tajima, “Abortions and Breast Cancer Risk in Premenopausal and Postmenopausal Women in Jiangsu Province of China,” //Asian Pacific Journal of Cancer Prevention//​ 13 (2012): 33-35. [[http://​www.apjcpcontrol.org/​page/​popup_paper_file_view.php?​pno=MzMtMzUgMTIuMiZrY29kZT0yNzAxJmZubz 0w&​pgubun=i]] ​(accessed ​December 7, 2012).)) found an increased risk associated with a history of induced abortion. Having two induced abortions or three or more induced abortions contributed to increased breast cancer risk, and an increasing number of induced abortions was associated with increased breast cancer risk. Premenopausal women and postmenopausal women seemed to be affected differently by induced abortion. The authors fail to demonstrate the differences between their cases and controls; their study may be marked by health or survivor bias; they do not assess the effect of induced abortion with regard to timing of first full-term pregnancy, maternal age, or gestational period; they do not show the influence of several breast cancer risk factors; and they fail to distinguish between first- and second-trimester spontaneous abortions.+A 2012 Chinese study of abortion and breast cancer risk((A.R. Jiang, C.M. Gao, J.H. Ding, S.P. Li, Y.T. Liu, H.X. Cao, J.Z. Wu, J.H. Tang, Y. Qian, and K. Tajima, “Abortions and Breast Cancer Risk in Premenopausal and Postmenopausal Women in Jiangsu Province of China,” //Asian Pacific Journal of Cancer Prevention//​ 13(2012): 33-35. ​Available at [[http://​www.apjcpcontrol.org/​page/​popup_paper_file_view.php?​pno=MzMtMzUgMTIuMiZrY29kZT0yNzAxJmZubz 0w&​pgubun=i]]. Accessed ​December 7, 2012.)) found an increased risk associated with a history of induced abortion. Having two induced abortions or three or more induced abortions contributed to increased breast cancer risk, and an increasing number of induced abortions was associated with increased breast cancer risk. Premenopausal women and postmenopausal women seemed to be affected differently by induced abortion. The authors fail to demonstrate the differences between their cases and controls; their study may be marked by health or survivor bias; they do not assess the effect of induced abortion with regard to timing of first full-term pregnancy, maternal age, or gestational period; they do not show the influence of several breast cancer risk factors; and they fail to distinguish between first- and second-trimester spontaneous abortions.
  
 The Jiang study included 669 cases identified at Jiangsu Province Cancer Hospital from visits between June 2004 and December 2007 and through cancer registries in Huian, Jintan, Wuxi, and Taixing, all in Jiangsu Province, China. Six hundred eighty-two controls were randomly identified in towns near Taixing, Wuxi, Jintan, and Huian. The Jiang study included 669 cases identified at Jiangsu Province Cancer Hospital from visits between June 2004 and December 2007 and through cancer registries in Huian, Jintan, Wuxi, and Taixing, all in Jiangsu Province, China. Six hundred eighty-two controls were randomly identified in towns near Taixing, Wuxi, Jintan, and Huian.
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 =====23. 2013 Huang Meta-Analysis===== =====23. 2013 Huang Meta-Analysis=====
  
-A 2013 meta-analysis in China((Yubei Huang et al., “A meta-analysis of the association between induced abortion ​and breast cancer risk among Chinese ​females,” //Cancer Causes and Control// (2013): 1-10.)) showed a statistically significant increased risk of breast cancer with abortion. This study references crude odds ratios rather than odds ratios adjusted for confounding breast cancer risk factors; a number of the articles referenced do not distinguish induced from spontaneous abortion; it does not assess abortions and live births temporally; and no significant effect for abortion is detected when the articles it deems of highest quality are assessed together.+A 2013 meta-analysis in China((Yubei Huang et al., “A Meta-analysis of the Association Between Induced Abortion ​and Breast Cancer Risk among Chinese ​Females,” //Cancer Causes and Control// (2013): 1-10.)) showed a statistically significant increased risk of breast cancer with abortion. This study references crude odds ratios rather than odds ratios adjusted for confounding breast cancer risk factors; a number of the articles referenced do not distinguish induced from spontaneous abortion; it does not assess abortions and live births temporally; and no significant effect for abortion is detected when the articles it deems of highest quality are assessed together.
  
 This meta-analysis references 36 articles from 14 provinces in China. This meta-analysis references 36 articles from 14 provinces in China.
  
-**__Health bias.__** As we do not have access to the majority of the articles referenced in the meta-analysis,​ it is impossible ​for us to determine whether or not health bias affected these studies. However, the authors note that “no significant associations between [induced abortion] and breast cancer were found in cohort studies ….”((Yubei Huang et al., “A meta-analysis of the association between induced abortion ​and breast cancer risk among Chinese ​females,” //Cancer Causes and Control// (2013): 6.)) As we note above in our explanation of health bias, it may be that health bias is most pernicious in cohort studies, depending on how their populations are selected.+**__Health bias.__** As this reference has no access to the majority of the articles referenced in the meta-analysis,​ it is impossible to determine whether or not health bias affected these studies. However, the authors note that “no significant associations between [induced abortion] and breast cancer were found in cohort studies ….”((Yubei Huang et al., “A Meta-analysis of the Association Between Induced Abortion ​and Breast Cancer Risk among Chinese ​Females,” //Cancer Causes and Control// (2013): 6.)) As noted above in the explanation of health bias, it may be that health bias is most pernicious in cohort studies, depending on how their populations are selected.
  
-Huang et al. also found, in response to their inquiry as to “whether inadequate choice of referent group” could skew the results of their analysis, that a lower percentage of women with induced abortions in the control group was associated with a higher odds ratio for induced abortion. Clearly, careful randomization of the control population is essential. Additionally,​ this finding is rather in parallel with the point that if authors introduce health bias into their analyses by eliminating from their case and control population women with a previous history of breast cancer—and who, according to our theory, disproportionately have a history of induced abortion—and thereby shrink ​thedisparity ​in the number of women with induced abortion history between cases and controls, they skew the odds ratio associated with induced abortion.+Huang et al. also found, in response to their inquiry as to “whether inadequate choice of referent group” could skew the results of their analysis, that a lower percentage of women with induced abortions in the control group was associated with a higher odds ratio for induced abortion. Clearly, careful randomization of the control population is essential. Additionally,​ this finding is rather in parallel with the point that if authors introduce health bias into their analyses by eliminating from their case and control population women with a previous history of breast cancer—and who, according to the theory, disproportionately have a history of induced abortion—and thereby shrink ​the disparity ​in the number of women with induced abortion history between cases and controls, they skew the odds ratio associated with induced abortion.
  
 This finding—that a higher rate of induced abortion in the control population diminishes the overall study’s odds ratio—is crucial to note, particularly given the very high (over 50 percent) prevalence of induced abortion in the control groups of many studies (both cohort studies, both studies conducted in Shanghai, and a number of the studies ranked as being of highest quality) in the subgroups whose collective analyses detected no significant influence for induced abortion. This finding—that a higher rate of induced abortion in the control population diminishes the overall study’s odds ratio—is crucial to note, particularly given the very high (over 50 percent) prevalence of induced abortion in the control groups of many studies (both cohort studies, both studies conducted in Shanghai, and a number of the studies ranked as being of highest quality) in the subgroups whose collective analyses detected no significant influence for induced abortion.
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 The authors also noted a possible bias toward underreporting of abortions, particularly among women who have procured more than two. They state that “this underestimation will inevitably create spurious associations between [induced abortion] and breast cancer, especially for more induced abortions.” The authors also noted a possible bias toward underreporting of abortions, particularly among women who have procured more than two. They state that “this underestimation will inevitably create spurious associations between [induced abortion] and breast cancer, especially for more induced abortions.”
  
-**__Induced abortion and quality of articles reviewed.__** The authors note that they ranked the articles in their meta-analysis by quality.((“The methodological quality of included studies was independently assessed by two reviews according to Newcastle-Ottawa Scale (NOS) based on three broad perspectives … (1) the selection of the study groups; (2) the comparability of the groups; and (3) the ascertainment of exposure or outcome of interest, with scores ranging from 0 to 9.” See Yubei Huang et al., “A meta-analysis of the association between induced abortion ​and breast cancer risk among Chinese ​females,” //Cancer Causes and Control// (2013): 3.)) Eight studies received an “A” ranking (a score of 8 or 9 on their quality scale), 24 studies received a “B” ranking (a score of 5 to 7), and two received a “C” ranking (a score of 4 or lower). When the “A”-ranked studies were analyzed together, Huang et al. detected no significant influence for induced abortion. A positive, significant influence on breast cancer was detected for induced abortion in the analysis of the “B”-ranked studies and the “C”-ranked studies.+**__Induced abortion and quality of articles reviewed.__** The authors note that they ranked the articles in their meta-analysis by quality.((“The methodological quality of included studies was independently assessed by two reviews according to Newcastle-Ottawa Scale (NOS) based on three broad perspectives … (1) the selection of the study groups; (2) the comparability of the groups; and (3) the ascertainment of exposure or outcome of interest, with scores ranging from 0 to 9.” See Yubei Huang et al., “A Meta-analysis of the Association Between Induced Abortion ​and Breast Cancer Risk among Chinese ​Females,” //Cancer Causes and Control// (2013): 3.)) Eight studies received an “A” ranking (a score of 8 or 9 on their quality scale), 24 studies received a “B” ranking (a score of 5 to 7), and two received a “C” ranking (a score of 4 or lower). When the “A”-ranked studies were analyzed together, Huang et al. detected no significant influence for induced abortion. A positive, significant influence on breast cancer was detected for induced abortion in the analysis of the “B”-ranked studies and the “C”-ranked studies.
  
 Induced abortion and other characteristics of studies reviewed. No significant influence was found for induced abortion when the cohort studies were analyzed as a group, but the collective analysis of the case-control studies found induced abortion to have a positive, significant influence on breast cancer risk. Induced abortion and other characteristics of studies reviewed. No significant influence was found for induced abortion when the cohort studies were analyzed as a group, but the collective analysis of the case-control studies found induced abortion to have a positive, significant influence on breast cancer risk.
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 **__Omitted variable bias.__** The Huang meta-analysis used crude odds ratios in its analyses rather than odds ratios adjusted for other factors that affect a woman’s breast cancer risk (e.g., age at first birth, parity). They state that they did this because, among other reasons, not all the examined studies released adjusted odds ratios, and where studies did, the factors for which the crude odds ratios were adjusted differed. **__Omitted variable bias.__** The Huang meta-analysis used crude odds ratios in its analyses rather than odds ratios adjusted for other factors that affect a woman’s breast cancer risk (e.g., age at first birth, parity). They state that they did this because, among other reasons, not all the examined studies released adjusted odds ratios, and where studies did, the factors for which the crude odds ratios were adjusted differed.
  
-Huang et al. add that the collective analysis of the 13 available adjusted odds ratios was close to their overall result based on the 36 crude odds ratios. They state that this “suggest[s] that the primary result was not substantially confounded by the un-adjusted factors.”((Yubei Huang et al., “A meta-analysis of the association between induced abortion ​and breast cancer risk among Chinese ​females,” //Cancer Causes and Control// (2013): 8.))+Huang et al. add that the collective analysis of the 13 available adjusted odds ratios was close to their overall result based on the 36 crude odds ratios. They state that this “suggest[s] that the primary result was not substantially confounded by the un-adjusted factors.”((Yubei Huang et al., “A Meta-analysis of the Association Between Induced Abortion ​and Breast Cancer Risk among Chinese ​Females,” //Cancer Causes and Control// (2013): 8.))
  
 **__Incomplete reporting and distinguishing between induced and spontaneous abortions.__** It seems some of the articles included in this meta-analysis do not distinguish between induced and spontaneous abortion. However, Huang et al. perform both joint and separate analyses of studies that do and do not analyze induced abortion alone. **__Incomplete reporting and distinguishing between induced and spontaneous abortions.__** It seems some of the articles included in this meta-analysis do not distinguish between induced and spontaneous abortion. However, Huang et al. perform both joint and separate analyses of studies that do and do not analyze induced abortion alone.
  
-The authors note as justification for including studies that do not distinguish between induced and spontaneous abortion that spontaneous abortion likely occurs in 4.26 to 5.27 percent of Chinese women.((Yubei Huang et al., “A meta-analysis of the association between induced abortion ​and breast cancer risk among Chinese ​females,” //Cancer Causes and Control// (2013): 5.)) By contrast, in many of the studies in the meta-analysis,​ (unspecified type) abortion occurred in the control groups at a rate of over “50 [percent], suggesting that abortions tended to be primarily [induced abortion] rather than [spontaneous abortion].((Yubei Huang et al., “A meta-analysis of the association between induced abortion ​and breast cancer risk among Chinese ​females,” //Cancer Causes and Control// (2013): 5.+The authors note as justification for including studies that do not distinguish between induced and spontaneous abortion that spontaneous abortion likely occurs in 4.26 to 5.27 percent of Chinese women.((Yubei Huang et al., “A Meta-analysis of the Association Between Induced Abortion ​and Breast Cancer Risk among Chinese ​Females,” //Cancer Causes and Control// (2013): 5.)) By contrast, in many of the studies in the meta-analysis,​ (unspecified type) abortion occurred in the control groups at a rate of over “50 [percent], suggesting that abortions tended to be primarily [induced abortion] rather than [spontaneous abortion].((Yubei Huang et al., “A Meta-analysis of the Association Between Induced Abortion ​and Breast Cancer Risk among Chinese ​Females,” //Cancer Causes and Control// (2013): 5.
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-This entry draws from [[http://​marri.us/​abortion-breast-cancer|Induced Abortion and Breast Cancer]].))+This entry draws from [[http://​marri.us/​research/​research-papers/​induced-abortion-and-breast-cancer/|Induced Abortion and Breast Cancer]].))