Treatment of HER2-positive cutaneous apocrine carcinoma of the axilla.

Cutaneous apocrine carcinoma (CAC) is an extremely rare skin appendage malignant tumor that develops in the apocrine sweat glands, and no evidence-based drug therapy has been established. A 61-year-old female patient was diagnosed with axillary CAC with axillary lymph node metastasis and underwent surgery. Pathological examination revealed seven lymph node metastases. Immunostaining revealed that the tumor cells were estrogen receptor (ER)-positive, progesterone receptor (PgR)-positive, and human epidermal growth factor receptor 2 (HER2)-positive. The patient received chemotherapy, including anti-HER2 drugs, and hormone therapy to prevent recurrence. No recurrence was observed for > 3 years after surgery. The apocrine glands in the skin and mammary glands have similar characteristics and mammary glands are thought to be modified or derived from the apocrine glands present in the subcutaneous adipose tissue. Therefore, ER, PgR, and HER2 levels may be positive in CAC. Drug treatments for breast cancer may also be effective for CAC.