Susan G Komen  
I've Been Diagnosed With Breast Cancer Someone I Know Was Diagnosed Share Your Story Join Us And Stay Informed Donate To End Breast Cancer
Home > Understanding Breast Cancer > Breast Cancer Research > Table 25: Abortion and breast cancer risk

  


Table 25: Abortion and breast cancer risk

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 have agreed the scientific evidence does not support a link between abortion and breast cancer [1-2]. The NCI routinely reviews the evidence on this topic (most recently in 2010) and continues to agree the evidence does not support a link between the two [3]).

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 these 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 bias study results.

Prospective cohort studies are much more likely to give accurate results on the topic of abortion. These studies gather 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.

Read our statement on abortion and breast cancer risk.   

Learn more about abortion and breast cancer risk.

Miscarriage and breast cancer risk

Further supporting the evidence on abortion, are findings from studies on miscarriage (also called spontaneous abortion) and the risk of breast cancer. Findings from cohort studies and a large pooled analysis have shown miscarriage does not increase the risk of breast cancer [4-10]. In 2003, the National Cancer Institute concluded miscarriage was not linked to breast cancer [1]. The NCI routinely reviews the evidence on this topic (most recently in 2010) 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 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. [11] 

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 [12]

92,767
(3,137 cases)

Yes

10

0.91
(0.82-0.99)

Rosenblatt et al. [13]

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 [14]

37,247
(1,369 cases)

 Yes

9

1.1
(0.8-1.6)

Danish Diet, Cancer and Health Study [15]

 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 analysis 

Collaborative Group on Hormonal Factors in Breast Cancer [10]

162,414
(43,866 cases)

Yes

 

0.93
(0.89-0.96)

* Relative risks for miscarriage were similar, 1.07 (0.99-1.14). 

† Mean follow-up time estimated from dates of study.

‡ Relative risks for miscarriage were 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). 

 

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 (reaffirmed 2011). Washington, DC: The American College of Obstetricians and Gynecologists. http://www.acog.org/Resources_And_Publications/Committee_Opinions/Committee_on_Gynecologic_Practice/Induced_Abortion_and_Breast_Cancer_Risk, 2011.
  3. National Cancer Institute. Abortion, miscarriage, and breast cancer risk. http://www.cancer.gov/cancertopics/factsheet/Risk/abortion-miscarriage, 2010.
  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. 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.
  12. 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.
  13. 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.
  14. Lazovich D, Thompson JA, Mink PJ, et al. Induced abortion and breast cancer risk. Epidemiology. 11(1):76-80, 2000.
  15. 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 08/30/13