Family history and oral contraceptives: unique relationships in breast cancer patients.

The relative frequency of a history of breast cancer among specific blood relatives was determined for breast cancer patients according to their prior use of oral contraceptives (OC). These data were compared with those derived from patients having various types of noninvasive breast lesions and from control women. It was found that a history of breast cancer among grandmothers or aunts was significantly more frequent among breast cancer patients who had used OC for one or more years continuously than among OC-negative breast cancer patients, and among patients with noninvasive breast lesions and control women, regardless of OC usage. Breast cancer patients whose grandmothers or aunts had breast cancer used OC significantly more frequently than did family history (FH)-negative breast cancer patients and breast cancer patients having a history of breast cancer limited to relatives other than grandmothers and aunts (mothers, sisters, cousins). It appears that the family history is a significant covariable in the relationship between OC usage and breast cancer. There is a need for specific studies to test the possibilities that OC usage increases the risk of breast cancer among women whose grandmothers or aunts had breast cancer, and reduces the risk of breast cancer in FH-negative women.