Pituitary adenoma and bilateral male breast cancer: an unusual association.

An unusual case is presented of bilateral breast cancer in a male patient with a long history of endocrine dysfunction due to a prolactinoma. The role of abnormal endocrine function in the development of male breast cancer is reviewed. The strongest association between aberrant endocrine function and male breast cancer occurs in patients with Klinefelter's syndrome, who have an approximate 3% lifetime risk of developing breast cancer. Retrospective case-control studies indicate that both estrogen excess and androgen deficiency may be involved in male breast cancer. Clinical studies of estrogen, androgen, and prolactin levels in male breast cancer patients have yielded conflicting results, and the precise nature of the hormonal mechanisms involved in the development of male breast cancer remains to be defined.