Oral contraceptive use in women with a family history of breast cancer.

To evaluate the effect of oral contraceptive use on the risk of breast cancer from 20-54 years of age in women with a family history of the disease, we analyzed data from the Cancer and Steroid Hormone Study of the Centers for Disease Control and the National Institute of Child Health and Human Development. For 2 years, beginning December 1980, the study enrolled from eight geographical areas in the United States 4730 women with breast cancer and 4646 controls who were breast cancer-free. For women with a first-degree family history of breast cancer, 554 cases and 280 controls, there was no evidence that use of oral contraceptives, even long-term, contributed to their risk of the disease. Neither total duration of use nor duration of use before first term pregnancy bore any relationship with breast cancer risk. Analyses designed to reveal a potential latent effect also showed no evidence of an adverse effect. For women with a second-degree family history of breast cancer, 777 cases and 595 controls, some isolated elevations in risk were observed for selected subgroups of oral contraceptive users. Detailed analyses of oral contraceptive formulation, the characteristics of the women involved, and the patterns of risk observed by latent period and duration of use suggest that these results, most within the limits of chance variation, are not likely to be a consequence of oral contraception.