Male breast gland has fewer, less developed lobules and rich tissue lymphatic network. Male breast cancer accounts for about 1% of the total, with an increasing trend year by year. Late age of onset (peak incidence 58y-64y), late detection (over 6 months delay, over 40% of patients are intermediate to late stage), long duration of disease, high rate of lymphatic metastasis (50% metastasis in anterior lymph nodes, multiple lymph nodes metastasis). It is more common in Blacks and Middle Eastern Jews. Pathology is predominantly ductal adenocarcinoma, with lobular carcinoma rare and often moderately differentiated. Estrogen-progestin receptor (ER, PR) expression is high 60%-70%. Etiology: family history, disorders of estrogen/androgen secretion (Klinefelter syndrome), history of breast development, BRCA2 gene mutation, Cowden syndrome (multiple malformations), heat, pollution, alcohol. Clinical manifestations include painless lumps under the nipple or areola, with distension, overflow, and skin ulcers, and tumors that tend to invade the skin and pectoral muscle. Examination: Ca15-3, CEA, ultrasound, mammography, MR, biopsy. Easily misdiagnosed as male breast development, sebaceous cyst, breast fibroid, lipoma, fat necrosis, abscess, etc. Treatment: (1) Radical surgery, modified radical surgery, mastectomy + axillary lymph node dissection; key points of surgery: large tension of incision, skin graft if necessary; modified radical surgery axillary lymph node dissection is more difficult; often accompanied by internal breast lymphatic metastasis. (2) Neoadjuvant chemotherapy and postoperative chemotherapy: metastatic cancer with lymphatic metastasis, primary tumor >1 cm, hormone receptor (-), anthracycline or combined with paclitaxel; (3) Endocrine therapy: triamcinolone for 5 years; aromatase inhibitor (letrozole) to suppress 50% estrogen level; (4) Local radiotherapy. Prognosis: 5-year survival rate >80% for stage I patients, 50%-80% for stage II, 30%-60% for stage III.