[Extramammary Paget's disease with a large mass in male genitalia: a case report].

A 57-year-old Japanese man presented with a mass 3 cm in diameter at the root of the penis. The patient had noticed the mass growing for 5 years, but had no pain or itching. Histological examination revealed it to be invasive Paget's disease, and the mass was resected along with skin of normal appearance within 3 cm around it. Regional lymph node metastasis was also revealed in the operation, and irradiation at the pelvic and inguinal region was done. Extramammary Paget's disease with a large mass is relatively rare, and invasive extramammary Paget's disease has a poor prognosis.