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studies_that_confirm_the_abortion-breast_cancer_link [2015/11/18 13:13]
marri [Studies that Confirm the Abortion-Breast Cancer Link]
studies_that_confirm_the_abortion-breast_cancer_link [2017/06/12 11:02] (current)
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 =====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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 **__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. **__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//​. 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 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 noted 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=====
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 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 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. **__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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 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 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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-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]].))