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Breast Cancer Risk From Abortions

Does abortion increase the risk of breast cancer?

10 January 1997

An unproven, but potential risk factor for breast cancer that many women don't talk about, but one that many may wonder about, is abortion. A recently published study on the subject provides strong evidence that induced abortion does not increase a woman's risk of breast cancer.

The type of abortion in question is induced abortion, rather than spontaneous abortion, which is generally known as a miscarriage. Previous studies examining this issue have yielded no clear answers, in part due to the private nature of abortion which may cause women to be reluctant to report it in interviews.

Abortion has been speculated to increase a woman's risk for breast cancer by abruptly altering the hormonal milieu, leaving the breast cells in a state of proliferation without pushing them to the final stage of differentiation which is thought to be protective.

The study published in the January 9, 1997 edition of the New England Journal of Medicine attempts, with some success, to settle the controversy around abortion as a risk factor for breast cancer. The study evaluated all Danish women born between April 1, 1935 and March 31, 1978 --1.5 million women in all. It used Denmark's sophisticated socialized medicine network to see if any of the women had induced abortions (reporting of induced abortions is mandatory and tracked through the National Registry of Induced Abortions) and if they developed breast cancer, which would be reported to the Danish Cancer Registry. After examining subgroups, such as age at time of abortion, number of children born, time since abortion, or age at diagnosis of breast cancer, the researchers concluded that induced abortions have no overall effect on the risk of breast cancer. However, the study included small numbers of women who had late-term abortions (later than five months) and very early abortions (earlier than seven weeks). The women with late term abortions had higher numbers of breast cancer than would be expected; the women with the early term abortions had fewer breast cancers.

What does this study mean to the general public? An editorial accompanying the article, written by Patricia Hartge, ScD, of the National Cancer Institute, pointed out that while questions remain for scientists trying to understand how pregnancy affects the development of breast cancer, women need not worry about the risk of breast cancer when facing the difficult decision of whether to terminate a pregnancy. With regard to higher rates of breast cancer in the women who underwent very late abortions, Dr. Hartge said that additional research will have to be done on larger numbers of such women to find answers. However, since the overwhelming majority of the abortions in the Danish study took place between seven to 14 weeks of gestation, which mirrors the timeframe when most US abortions take place, the results point to a null effect on abortion and its impact on developing breast cancer.

Officials at the American Cancer Society point out that this study has a number of strengths, including the quality of data on induced abortions (which avoided reliance on the study participants to accurately report their histories) and its large size. However, since new evidence can turn up in additional studies, they stop short of calling this study definitive, instead noting that it "strongly suggests any meaningful cause-effect relationship between induced abortion and breast cancer is unlikely to exist."

Source: Melbye M, Wohlfahrt J, Olsen JH, et al. Induced abortion and the risk of breast cancer. NEJM, 1997;336:(2) 81-85. Editorial: Hartge P. Abortion, breast cancer, and epidemiology. NEJM, 1997;336:(2) 127-128.