A case of polypoid clear cell acanthoma on the scrotum.

A red nodule appeared on the left side of the scrotum of a 37-year-old Japanese man and slowly grew for four years. When he first visited us, it was 5 mm in diameter, polypoid shaped, and had a smooth and slightly moist surface. Histologically, acanthosis, parakeratosis, and dilated blood vessels were seen in the upper dermis. In higher magnification, the thick epidermis consisted of tumor cells with slightly enlarged nuclei and pale cytoplasm, and neutrophils were also seen among the tumor cells. The cytoplasm of the tumor cells was stained with periodic-acid-Schiff (PAS), and the positive reaction was digested by diastase. There has been no previous report of polypoid clear cell acanthoma in Japan, and only a few reports from the rest of the world. In addition, clear cell acanthoma arising on the scrotum is particularly unusual.