A case of ductal sweat gland carcinoma connected to syringocystadenoma papilliferum arising in nevus sebaceus.

We report a case of a tumor arising in the preauricular region in a 50-year-old woman. The histopathological findings revealed it to be a ductal sweat gland carcinoma connected to a syringocystadenoma papilliferum (SCAP) arising in a nevus sebaceus. Mucinous stroma, considered to be deposition of hyaluronic acid, was also observed in the ductal carcinoma portion. The immunohistochemical and ultrastructural findings in the ductal carcinoma were compared with those in the SCAP. The proliferating cell nuclear antigen labeling index of the cells in the ductal carcinoma was higher than that of those in the SCAP. Both the ductal sweat gland carcinoma and SCAP showed findings compatible with the ductal segment of a sweat gland.