Abortion and breast cancer risk.

The relationship between spontaneous and induced abortions and breast cancer risk was analyzed using data from a case-control study conducted between June 1991 and February 1994 in 6 Italian centers on 2,569 histologically confirmed incident breast cancer cases and 2,588 controls admitted to hospital for a wide range of acute, non-neoplastic, non-hormone-related diseases. One or more abortions were reported by 31% of cases and 32% of controls, corresponding to a multivariate odds ratio (OR) of 1.0 (95% confidence interval [CI], 0.8-1.1). No trend in risk was observed with increasing number of total abortions or spontaneous and induced abortions separately. No significant relationship was found between the risk of breast cancer and history of spontaneous or induced or total abortions in separate strata of age at diagnosis, number of children, time of abortion in relation to first birth and family history of breast cancer. When abortion was the outcome of the first pregnancy, the OR was 1.2 for spontaneous and 1.3 for induced abortion, in relation to women with birth as outcome of the first pregnancy, and 1.0 and 1.1, respectively, when the reference category was nulligravidae. Thus, our results indicate a lack of association between induced and spontaneous abortions and breast cancer risk.