Endocrinology of gynaecomastia.

Gynaecomastia is the most common disorder of the male breast. It can occur at any age, and for this reason laboratory investigations may be requested by clinicians from many specialties. Gynaecomastia may occur transiently in neonates. It may also occur transiently during puberty, when it is common and generally benign. It must, however, be regarded as unusual in prepubertal children and all young and middle-aged men. Although iatrogenic and benign gynaecomastia are common in the elderly, further investigations may still be justified since breast cancer or other neoplasm must be ruled out. Biochemical investigations, when warranted, are aimed at establishing an underlying cause. Endocrine investigations might include serum oestradiol (or oestrone if available), testosterone, luteinizing hormone, sex-hormone-binding globulin, human chorionic gonadotrophin, prolactin and thyroid function tests. In this review, the source and role of oestrogens in men, the androgen oestrogen dynamics, the causes and clinical entities of gynaecomastia, and interpretation of laboratory tests are described.