Syringocystadenocarcinoma papilliferum: case report and immunohistochemical comparison with its benign counterpart.

Syringocystadenocarcinoma papilliferum (SCACP) is the malignant counterpart of syringocystadenoma papilliferum (SCAP), although only a few cases have been reported in the literature and its clinical and histologic characteristics are not well known. We report a case of SCACP that started as an enlarging nodule over 10 years in the perianal area of a 61-year-old man. Macroscopically, the lesion was a black exophytic tumor, 6 cm in diameter, with a granular surface. Histologically, it was an in situ adenocarcinoma, showing cytologic atypia and pagetoid spread in the surrounding epithelia, although the clinicopathologic features were distinct from extramammary Paget's disease. The tumor lacked the typical double-layered pattern of SCAP but had some similar histopathologic features to SCAP. Decapitation secretion was apparent and there was positive immunoreactivity to epithelial membrane antigen and human milk fat globules subclass 2. SCACP is a rare cutaneous tumor but nevertheless represents a specific dermatopathologic entity.