THE RISK OF BREAST-CANCER FOLLOWING SPONTANEOUS OR INDUCED-ABORTION

To evaluate the relationship between breast cancer risk and spontaneou s and induced abortion, we conducted a detailed descriptive review of 32 epidemiologic studies that provided data by type of abortion and by various measures of exposure to abortion - number of abortions, timin g of abortion in relation to first full-term pregnancy, length of gest ation, and age at first abortion. Breast cancer risk did not appear to be associated with an increasing number of spontaneous or induced abo rtions. Our review also suggested that breast cancer risk probably was not related to the other measures of exposure to abortion, and probab ly did not differ by age or a family history of breast cancer. Finally , the data appeared to suggest a slightly increased risk among nullipa rous women, but this tendency was based primarily on studies with a sm all number of nulliparous women who had had spontaneous or induced abo rtions. Definitive conclusions about an association between breast can cer risk and spontaneous or induced abortion are not possible at prese nt because of inconsistent findings across studies. Future investigati ons should consider prospective designs, separate analyses of spontane ous and induced abortions, appropriate referent groups, and adequate a djustment for confounding and effect modification. Future investigatio ns also should attempt to determine whether any increased risks reflec t the transient increase in breast cancer risk hypothesized for full-t erm pregnancy or a causal relationship specific to spontaneous or indu ced abortion.