Abortion not a factor in breast cancer risk.

A large prospective study of U.S. women has found no association between induced or spontaneous abortion and the incidence of breast cancer. (1) The Nurses' Health Study II has been following a cohort of 25-42-year-old nurses enrolled in 1989 through questionnaires mailed every two years; to assess the relationship between abortion and breast cancer, researchers analyzed data from questionnaires completed between 1993, when information on induced and spontaneous abortion was first collected, and 2003. During the study period, 1,458 cases of breast cancer were identified among the 105,716 participants; hazard analyses adjusting for a wide range of risk factors revealed that women who had had an induced abortion or miscarriage were at no greater risk than others. Breast cancer incidence also showed no association with number of induced abortions, women's age at induced abortion, parity or timing of abortion. The investigators caution that the results may not be applicable to postmenopausal women. However, they note that the prospective cohort study design avoids some of the pitfalls of earlier work on this issue, which has generally been based on case-control or retrospective studies, and therefore bolsters the importance of the findings.

(1.) Michels KB et al., Induced and spontaneous abortion and incidence of breast cancer among young women, Archives of Internal Medicine, 2007, 167(4):814 820.