This summary table contains detailed information about research studies. While viewing summary tables offers an informative glimpse at the science behind many breast cancer guidelines and recommendations, they should be viewed with some caution. There are a number of concepts you must understand to be able to successfully read and interpret research tables. To get some background information about understanding research tables, please see How to Read a Research Table.
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Introduction: Although there has been some controversy in the past about the relationship between abortion (also called induced abortion) and breast cancer risk, the current body of evidence clearly shows no link between the two. In 2003, the National Cancer Institute’s Board of Scientific Advisors and Board of Scientific Counselors unanimously agreed that scientific evidence does not support any link between abortion and breast cancer [1]. Later that same year, the American College of Obstetricians and Gynecologists also stated that there was no evidence to support a link between the two [2].
While many case-control studies have suggested that abortion may increase the risk of breast cancer [3], the nature of these studies makes the accuracy of their results questionable. Case-control studies rely on the reporting of past behavior. When it comes to a sensitive topic 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 can compromise study results.
Prospective cohort studies, however, are much more likely to give accurate results on the topic of abortion. These studies gather such sensitive information before women are diagnosed with breast cancer. This helps limit biased reporting. The large cohort studies listed below show that abortion does not increase the risk of breast cancer.
Further supporting these findings are cohort studies and a large pooled analysis that looked at the relationship between miscarriage (sometimes called spontaneous abortion) and breast cancer. Each of these studies showed that miscarriage does not increase the risk of breast cancer [6-14]. In 2003, the National Cancer Institute concluded that miscarriage is not linked to risk of breast cancer [1].
Find more information on 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: Available prospective cohort studies and pooled analyses.
Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
Study
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Study Population
(number of participants)
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Method by which Abortion History was Gathered
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Follow-up
(years)
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Relative Risk of Breast Cancer in Women Who Have Had an Abortion Compared to Women Who Have Not,
RR (95% CI)
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Prospective cohort studies
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Melbye et al. [6]
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1,529,512
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National abortion registry list (Denmark)
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24
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1.0
(0.94-1.1)
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Rosenblatt et al. [7]
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267,400
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Baseline questionnaire, before any breast cancer diagnoses
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8*
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1.01
(0.92-1.12)
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EPIC Study [8]
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267,361
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Baseline questionnaire, before any breast cancer diagnoses
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6.6
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0.95
(0.87-1.03)†
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California Teachers Study [9]
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109,893 |
Baseline questionnaire, before any breast cancer diagnoses
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9
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Among women with
no children:
0.95
(0.76-1.18)
Among women with children:
1.05
(0.92-1.20)
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Nurses' Health Study II [10]
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105,716
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Baseline and subsequent questionnaires before any breast cancer diagnoses
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10
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1.01
(0.88-1.17)‡
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E3N Cohort Study-France [11]
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92,767
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Baseline questionnaire, before any breast cancer diagnoses
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9.6
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0.91
(0.82-0.99)
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Harris et al. [12]
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49,000
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National abortion registry list (Sweden)
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18
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0.80
(0.58-0.99)
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Black Women's Health Study [13]
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54,000 (approx.)
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Baseline and subsequent questionnaires before any breast cancer diagnoses
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2-4
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Among women with
no children:
0.9
(0.5-1.4)§
Among women with children:
1.1
(0.8-1.4)§
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Iowa Women's Health Study [14]
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37,247
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Baseline questionnaire, before any breast cancer diagnoses
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9
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1.1
(0.8-1.6)
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Pooled analysis
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Collaborative Group on Hormonal Factors in Breast Cancer [15]
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43,866
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Various
(before cancer diagnosis)
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0.93
(0.89-0.96)
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* Estimate of mean follow-up time calculated from reported dates of study.
† Relative risks are for induced abortion. Relative risks for spontaneous abortion (miscarriage) were similar (1.07 (0.99-1.14)).
‡ Relative risks are for induced abortion. Relative risks for spontaneous abortion (miscarriage) were similar (0.89 (0.78-1.01)).
§ Relative risks are for induced abortion. Relative risks for spontaneous abortion (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)).
References
1. National Cancer Institute. Summary report: Early Reproductive Events and Breast Cancer Workshop. Washington, DC: National Cancer Institute, U.S. National Institutes of Health. http://cancer.gov/cancerinfo/ere-workshop-report, 2003.
2. The American College of Obstetricians and Gynecologists. News release: July 31, 2003. Washington, DC: The American College of Obstetricians and Gynecologists. http://www.acog.org/from_home/publications/press_releases/nr07-31-03-2.cfm?, 2003.
3. Brind J, Chinchilli VM, Severs WB, Summy-Long J. Induced abortion as an independent risk factor for breast cancer: a comprehensive review and meta-analysis. J Epidemiol Community Health. 50(5):481-96, 1996
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. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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.
12. Harris B-ML, Eklund G, Meirk O, et al. Risk of cancer of the breast after legal abortion during the first trimester: a Swedish registry study. Br Med J. 299(6713):1430-1432, 1989.
13. 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.
14. Lazovich D, Thompson JA, Mink PJ, et al. Induced abortion and breast cancer risk. Epidemiology. 11(1):76-80, 2000.
15. 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.
Updated 12/18/09
