Familial male breast cancer.

Infiltrating ductal carcinoma of the breast occurred in a total of six men from two families. In one family specimens from three men who had prophylactic mastectomies revealed focal intraductal hyperplasia, suggesting a familial tendency toward proliferation of mammary-duct epithelium. In the other family, benign and malignant breast lesions also developed in several women. Preliminary data suggest elevated urinary oestrogen excretion in three men from these families, implicating a defect in oestrogen production or metabolism in the pathogenesis of male breast neoplasms.