3.53

Abortion and Breast Cancer

Although it has been the subject of extensive research, there is no convincing evidence of a direct relationship between breast cancer and either induced or spontaneous abortion. Available data are inconsistent and inconclusive, with some studies indicating small elevations in risk, and others showing no risk associated with either induced or spontaneous abortions. The scientific rationale for an association between abortion and breast cancer is based on limited experimental data in rats, and is not consistent with human data.

Studies that have attempted to evaluate the association between abortion and breast cancer have been limited by small numbers of study subjects, questions of comparability between the study groups, inability to separate induced abortions and spontaneous abortions, and incomplete knowledge of other potentially pertinent lifestyle factors. Perhaps the most serious potential weakness relates to the possible inaccuracy of reporting of abortions in retrospect by study participants. Indeed, results from a study that examined the accuracy of reporting abortions indicate that women with breast cancer are more likely to accurately report having had an abortion than women without breast cancer, possibly leading to a false association between abortion and breast cancer.

For example, an article published by Daling and others in the Journal of the National Cancer Institute illustrates the difficulty of drawing conclusions. Daling studied the relationship between breast cancer and abortion for young women. The results, based on self-reports of abortions, indicate that induced abortion was associated with 1.5 times the average risk of developing breast cancer. Some inconsistencies in the findings of the Daling study were puzzling, as risk did not vary consistently with number of abortions, woman's age at abortion or length of pregnancy, nor did the study show an increase in risk associated with spontaneous abortions. An accompanying commentary by Rosenberg, in the same journal, concluded that "While the findings of Daling et al. add to the limited evidence that induced abortion increases the risk of breast cancer, neither a coherent body of knowledge nor a convincing biologic mechanism has been established." At the time of publication, the National Cancer Institute also released a press statement regarding the article, concluding that "Taken together, the inconsistencies and scarcity of existing research do not permit scientific conclusions."

A study published in the Journal of the National Cancer Institute found a 90-percent increased risk for breast cancer after an induced abortion. However, Matti A. Rookus and Flora E. van Leeuwen of The Netherlands Cancer Institute suggest that this figure may have been influenced by reporting bias attributed to the underreporting of abortion by healthy control subjects in the largely Catholic southeastern region of The Netherlands. In the western regions of the country, the association between abortion and breast cancer was statistically insignificant. Rookus and Leeuwen conclude that their "study does not support an appreciably increased risk for breast cancer after an induced abortion."

The most recent study of this question, which appears in The New England Journal of Medicine, provides important new evidence to resolve the controversy. In a large scale epidemiologic study, Mads Melbye et al. determined that the risk of developing breast cancer for women with a history of induced abortion is no different than the risk for women without such a history. Melbye et al. conclude that "induced abortions have no overall effect on the risk of breast cancer." This study relies on uniformly collected data on abortion in Danish registries before the diagnosis of breast cancer was made, thus avoiding the reporting bias of previous studies in which women may have been more likely to provide an inaccurate history of their abortions depending on whether or not they had breast cancer.

The risk of breast cancer increases with age, from about 1 in 2,525 for a woman in her thirties to about 1 in 11 for a woman during her seventies. Risk factors include a family history of breast cancer, early age at menarche, late age at menopause, late age at the time of the first full-term birth of a child, obesity, and certain breast conditions. The increased risk of developing breast cancer associated with each factor varies, from 1.5 to 4 times average risk.

It is important that women discuss their individual risk of breast cancer with their physicians.

To ensure that you have the most up to date information, please call the Cancer Information Service (CIS). The CIS, a program of the National Cancer Institute, is a nationwide telephone service for cancer patients and their families, the public, and health care professionals. CIS information specialists have extensive training in providing up-to-date and understandable information about cancer. They can answer questions in English and Spanish and can send free printed material. In addition, CIS offices serve specific geographic areas and have information about cancer-related services and resources in their region. The toll-free number of the CIS is 1-800-4-CANCER (1-800-422-6237).

References

1. Brinton LA, Hoover R, Fraumeni JF. Reproductive factors in the aetiology of breast cancer. Br J Cancer 1983;47:757-762.

2. Daling JR, Malone KE, Voigt LF, et al. Risk of breast cancer among young women: Relationship to induced abortion. J Natl Cancer Inst 1994;86:1584-1592.

3. Gammon MD, Bertin JE, Terry MB. Abortion and the risk of breast cancer: Is there a believable association? JAMA 1996;4:275:321-322.

4. Kelsey JL, Gammon MD, John EM. Reproductive factors and breast cancer. Epidemiol Rev 1993;15:36-47.

5. Kelsey JL. Breast cancer epidemiology: Summary and future directions. Epidemiol Rev 1993;15:256-263.

6. Lindefors-Harris BM, Eklund G, Adami HO, Meirik O. Response bias in a case- control study: Analysis utilizing comparative data concerning legal abortions from two independent Swedish studies. Am J Epidemiol 1991;134:1003-1008.

7. Melbye M, Wohlfahrt M, Olsen JH et al. Induced abortion and the risk of breast cancer. N Engl J of Med 1997;336:81-5.

8. Parazzini F, La Vecchia C, Negri E. Spontaneous and induced abortions and risk of breast cancer. Int J Cancer 1991;48:816-820.

9. Remennick LI. Induced abortion as cancer risk factor: A review of the epidemiological evidence. J Epidemiol Community Health 44:259-264, 1990.

10. Rookus, MA, van Leeuwen, FE. Induced Abortion and Risk for Breast Cancer: Reporting (Recall) Bias in a Dutch Case-Control Study. J Natl Cancer Inst 1996;88:1759-64

11. Rosenberg L, Palmer JR, Kaufman DW, Strom BL, Schottenfeld D, Shapiro S. Breast cancer in relation to the occurrence and the time of the induced and spontaneous abortion. Am J Epidemiol 1988;127:981-989.

12. Rosenberg L. Induced abortion and breast cancer: More scientific data are needed. J Natl Cancer Inst 1994;86:1569-1570.

13. Tavani A, Vecchia C, Franceshi S, et al. Abortion and Breast Cancer Risk. International Journal of Cancer 1996;65:401-405.

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