Research table: Abortion and breast cancer risk

This summary table contains detailed information about research studies. Summary tables are a useful way to look at the science behind many breast cancer guidelines and recommendations. However, to get the most out of the tables, it’s important to understand some key concepts. Learn how to read a research table.

Introduction: Research clearly shows abortion (also called induced abortion) is not linked to an increased risk of breast cancer.

The American College of Obstetricians and Gynecologists (ACOG) and the National Cancer Institute (NCI) routinely review the evidence on abortion and breast cancer. Since 2003, they have agreed the scientific evidence does not support a link between abortion and breast cancer [1-3].

In 2021, ACOG reaffirmed their conclusion there’s no link between abortion and breast cancer.

The importance of study design for research on abortion and breast cancer risk

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 their 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.

Large, prospective cohort studies show women who’ve had an abortion do not have an increased risk of breast cancer (see table below).

Learn more about abortion and breast cancer risk.

Miscarriage and breast cancer risk

Further supporting the evidence that abortion is not linked to an increased risk of breast cancer are findings from studies on miscarriage (also called spontaneous abortion). Findings from cohort studies, a meta-analysis and a large pooled analysis show women who’ve had a miscarriage do not have an increased risk of breast cancer [4-11].

Since 2003, the NCI has concluded miscarriage is not linked to breast cancer [2-3]. The NCI routinely reviews the evidence on this topic and continues to agree the evidence does not support a link between the two [3].

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	Study Population (number of participants)	Was Abortion History Gathered Before Breast Cancer Diagnosis?	Follow-up (years)	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. [12]	1,529,512 (10,246 cases)	Yes	24	1.0 (0.94-1.1)
EPIC Study [6]	267,361 (4,805 cases)	Yes	7	0.95 (0.87-1.03)*
California Teachers Study [7]	109,893 (3,324 cases)	Yes	9	Among women with no children: 0.95 (0.76-1.18) Among women with children: 1.05 (0.92-1.20)
E3N Cohort Study-France [13]	92,767 (3,137 cases)	Yes	10	0.91 (0.82-0.99)
Rosenblatt et al. [14]	267,400 (1,643 cases)	Yes	8†	1.01 (0.92-1.12)
Nurses’ Health Study II [8]	105,716 (1,458 cases)	Yes	10	1.01 (0.88-1.17)‡
Iowa Women’s Health Study [15]	37,247 (1,369 cases)	Yes	9	1.1 (0.8-1.6)
Danish Diet, Cancer and Health Study [16]	25,576 (1,215 cases)	Yes	12	Among women with children: 0.95 (0.83-1.09)§
Black Women’s Health Study [9]	54,000 (approx.) (348 cases)	Yes	2-4	Among women with no 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 [10]	162,414 (43,866 cases)	Yes		0.93 (0.89-0.96)
Guo et al. [11]	14 studies (12,481 cases)	Yes		1.00 (0.94-1.05)**

* Relative risk for miscarriage was similar, 1.07 (0.99-1.14).

† 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 women had an abortion before their first childbirth or after their first childbirth, with relative risks of 0.86 (0.65-1.14) and 0.97 (0.84-1.13), 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).

References

1. The American College of Obstetricians and Gynecologists. Induced abortion and breast cancer risk (reaffirmed in 2021). https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2009/06/induced-abortion-and-breast-cancer-risk, 2021.
2. National Cancer Institute. Abortion, miscarriage and breast cancer risk: 2003 workshop. https://www.cancer.gov/types/breast/abortion-miscarriage-risk#summary-report, 2010.
3. National Cancer Institute. Reproductive history and cancer risk. https://www.cancer.gov/about-cancer/causes-prevention/risk/hormones/reproductive-history-fact-sheet#is-abortion-linked-to-breast-cancer-risk, 2016.
4. Sellers TA, Potter JD, Severson RK, et al. Difficulty becoming pregnant and family history as interactive risk factors for postmenopausal breast cancer: the Iowa Women’s Health Study. Cancer Causes Control. 4(1):21-8, 1993.
5. Calle EE. Mervis CA. Wingo PA. et al. Spontaneous abortion and risk of fatal breast cancer in a prospective cohort of United States women. Cancer Causes Control. 6(5):460-8, 1995.
6. Reeves GK, Kan SW, Key T, et al. Breast cancer risk in relation to abortion: Results from the EPIC study. Int J Cancer. 119(7):1741-5, 2006.
7. Henderson KD, Sullivan-Halley J, Reynolds P, et al. Incomplete pregnancy is not associated with breast cancer risk: the California Teachers Study. Contraception. 77(6):391-6, 2008.
8. Michels KB, Xue F, Colditz GA, Willett WC. Induced and spontaneous abortion and incidence of breast cancer among young women: a prospective cohort study. Arch Intern Med. 167(8):814-20, 2007.
9. Palmer JR, Wise LA, Adams-Campbell LL, Rosenberg L. A prospective study of induced abortion and breast cancer in African-American women. Cancer Causes Control. 15(2):105-11, 2004.
10. Beral V, Bull D, Doll R, Peto R, Reeves G; Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83,600 women with breast cancer from 16 countries. Lancet. 363(9414):1007-16, 2004.
11. Guo J, Huang Y, Yang L, et al. Association between abortion and breast cancer: an updated systematic review and meta-analysis based on prospective studies. Cancer Causes Control. 26(6):811-9, 2015.
12. Melbye M, Wohlfahrt J, Olsen JH, et al. Induced abortion and the risk of breast cancer. N Engl J Med. 336(2):81-5, 1997.
13. Paoletti X, Clavel-Chapelon F. Induced and spontaneous abortion and breast cancer risk: results from the E3N cohort study. Int J Cancer. 106(2):270-6, 2003.
14. Rosenblatt KA, Gao DL, Ray RM, et al. Induced abortions and the risk of all cancers combined and site-specific cancers in Shanghai. Cancer Causes Control. 17(10):1275-80, 2006.
15. Lazovich D, Thompson JA, Mink PJ, et al. Induced abortion and breast cancer risk. Epidemiology. 11(1):76-80, 2000.
16. Braüner CM, Overvad K, Tjønneland A, Attermann J. Induced abortion and breast cancer among parous women: a Danish cohort study. Acta Obstet Gynecol Scand. 92(6):700-5, 2013.

Updated 06/05/24