Gynecomastia is a common clinical condition. It is generally considered to be palpable in men except for 3 conditions: transient mastopexy in newborns, enlarged mammary glands during puberty and occasional mastopexy occurring in older men. 1. Etiology All mammary gland development in men is due to increased estrogen secretion or a lower androgen/estrogen ratio. Excessive estrogen is the main cause of gynecomastia. Exogenous estrogen preparations given to men, such as prostate cancer patients treated with estrogen, long-term use of estrogen in transsexual men and excessive secretion of estrogen from adrenal or testicular tumors can lead to gynecomastia. Qian Mingping, General Surgery Department, Shanghai Tenth People’s Hospital 2. Clinical manifestations Men present with unilateral or bilateral palpable breast tissue in the form of disc-shaped nodules or diffuse enlargement, sometimes accompanied by enlarged nipples and areolas. Local discomfort or tenderness may be felt, and in a few patients, a small amount of white discharge is seen when the nipple is squeezed. If you have a pathological gynecomastia caused by an organic disease, you should also have the clinical manifestations of the original disease. 3. Laboratory tests (1) Gonadotropin measurement, gonadotropin measurement: help to diagnose whether there is primary or secondary hypospadias. (2) Liver and kidney function tests: help to diagnose liver and kidney failure. (3) Cortisol and ACTH, 17-OHP, blood and urine cortisol assay: can evaluate congenital and congenital adrenal cortical hyperplasia. (1) Breast ultrasound and mammography can differentiate between fat and breast tissue to rule out breast cancer in time. (2) Histopathological examination of the breast to further confirm the diagnosis. 4. Diagnosis First of all, it is necessary to determine whether the breast tissue is real or not. In men, mammary gland development should be a firm, palpable subareolar breast tissue with a free base and a diameter of >2 cm. Fatty breast deposits are common in obese men, which look like mammary gland development but have no glandular tissue. Mammography or ultrasonography can distinguish between fat and breast tissue. The next step is to rule out breast cancer, which is very rare in men. Cancer occurs slightly more frequently in men with gynecomastia than in normal men, with an incidence of about 0.4%. If the surface of breast tissue is not smooth, irregular growth and hard texture, it often indicates early stage cancer, and local ulcers or enlarged adjacent lymph nodes are signs of advanced breast cancer. 5.Differential diagnosis Understanding the patient’s medication history can help determine drug-induced gynecomastia. Physical examination including secondary sexual characteristics, testes and body type, plus sex hormone and gonadotropin measurements can help diagnose primary or secondary hypospadias. Liver and renal function tests help to diagnose liver and renal failure. Cortisol and ACTH, 17-OHP, and blood and urine cortisol measurements can rule out congenital adrenocortical hyperplasia. If the results of all the above tests are normal, the diagnosis of idiopathic gynecomastia can be made. 6. Treatment Dihydrotestosterone enanthate 200mg, injected intramuscularly once every 3-4 weeks. Tamoxifen can bind to estrogen receptors in target tissues and block the action of estrogen. The mechanism of action of clomiphene is similar to that of tamoxifen. Testosterone lactone inhibits aromatase, blocking the peripheral conversion of testosterone to E2. Mastopexy is still an important treatment for this disease due to the irreversibility of the long-term delay of gynecomastia.