Breast cancer risks in relatives of male breast cancer patients.

BACKGROUND: Previous studies have provided conflicting results concerning the familial effect of male breast cancer on breast cancer risks in female relatives. PURPOSE: We studied breast cancer risks in first-degree relatives of male patients and compared them with relatives of female patients. METHODS: Our study included 88 consecutively ascertained male patients and 320 of their first-degree relatives as well as 186 consecutively ascertained female patients and 633 of their first-degree relatives. Observed numbers of breast cancers in relatives were compared with the expected number derived from the Connecticut Tumor Registry. Multiple logistic regression analysis was also performed. RESULTS: Relatives of male patients exhibited a significant twofold increased risk when compared with expected rates and no difference in risk when compared with that of relatives of female patients. Prostate cancer in the family of a male patient resulted in a significant fourfold increased breast cancer risk compared with a risk of 1.4 in families with no history of prostate cancer. A family history of lung cancer, colon cancer, or melanoma had no effect on increasing risks of breast cancer. CONCLUSION: The familial effect of male breast cancer is the same as that of female breast cancer. IMPLICATIONS: Any estimates of breast cancer risk provided to individuals should also consider the occurrence of prostate cancer in the family, since prostate cancer appears capable of at least doubling the underlying twofold risk.