This summary table contains detailed information about research studies. Summary tables offer an informative look at the science behind many breast cancer guidelines and recommendations. However, they should be viewed with some caution. In order to read and interpret research tables successfully, it is important to understand some key concepts. Learn how to read a research table.
Introduction: Research clearly shows abortion (also called induced abortion) does not increase the risk of breast cancer.
Since 2003, the National Cancer Institute (NCI) and the American College of Obstetricians and Gynecologists (ACOG) have agreed the scientific evidence does not support a link between abortion and breast cancer [1-2].
The NCI and ACOG routinely review the evidence on this topic (most recently in 2016 and 2015, respectively) and continue to agree there is no link between abortion and breast cancer [1-2].
Some case-control studies have suggested abortion may increase the risk of breast cancer. However, the design of case-control studies makes the accuracy of these results questionable.
Case-control studies rely on the reporting of past behavior. When it comes to a sensitive subject like abortion, this can have a big impact on the information gathered.
The cases in these studies (the women with breast cancer) may be much more likely to give complete information about their abortion history than the controls (the women without breast cancer). Such differences in reporting bias study results.
Prospective cohort studies are much more likely to give accurate results on topics such as abortion. These studies gather sensitive information before women are diagnosed with breast cancer. This helps limit biased reporting.
The large cohort studies below show abortion does not increase the risk of breast cancer.
Learn more about abortion and breast cancer risk.
Further supporting the evidence that abortion does not increase breast cancer risk are findings from studies on miscarriage (also called spontaneous abortion) and the risk of breast cancer. Findings from cohort studies, a meta-analysis and a large pooled analysis show miscarriage does not increase the risk of breast cancer [3-10].
Since 2003, the NCI has concluded miscarriage is not linked to breast cancer .
The NCI routinely reviews the evidence on this topic (most recently in 2016) and continues to agree the evidence does not support a link between the two .
Learn about the strengths and weaknesses of different types of studies.
See how this risk factor compares with other risk factors for breast cancer.
Study selection criteria: Prospective cohort studies with at least 300 breast cancer cases, meta-analyses and pooled analyses.
Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
Study Population(number of participants)
Was Abortion History Gathered Before Breast Cancer Diagnosis?
Relative Risk of Breast Cancer in Women who Have Had an Abortion Compared to Women who Have Not, RR (95% CI)
Prospective cohort studies
Melbye et al. 
EPIC Study 
California Teachers Study 
Among women withno children:0.95(0.76-1.18)
Among women with children:1.05(0.92-1.20)
E3N Cohort Study-France 
Rosenblatt et al. 
Nurses' Health Study II 
Iowa Women's Health Study 
Danish Diet, Cancer and Health Study 
25,576 (1,215 cases)
Among women with children: 0.95 (0.83-1.09)§
Black Women's Health Study 
54,000 (approx.)(348 cases)
Among women withno children:0.9(0.5-1.4)¶
Among women with children: 1.1(0.8-1.4)¶
Pooled and meta-analyses
Collaborative Group on Hormonal Factors in Breast Cancer 
Guo et al. 
14 studies(12,481 cases)
† Mean follow-up time was estimated from dates of the study.
‡ Relative risk for miscarriage was similar, 0.89 (0.78-1.01).
§ All women in this study had children. Results were similar whether childbirth was before or after an abortion, with relative risks of 0.97 (0.84-1.13) and 0.86 (0.65-1.14), respectively.
¶ Relative risks for miscarriage were similar among women with no children, 1.0 (0.5-1.9), and among women with children, 1.1 (0.8-1.4).
** Relative risk for miscarriage was similar, 1.02 (0.95-1.09).
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