Apocrine poroma: a distinctive case in a patient with nevoid basal cell carcinoma syndrome

Traditionally, poromas have been classified as eccrine neoplasms, but several recent reports of poroid tumors with sebaceous, follicular, and apocrine differentiation have challenged this idea. In support of alternative differentiation, a case of an "apocrine" poroma is reported in a 19-year-old man with the nevoid basal cell carcinoma syndrome. A papule on the right cheek, thought clinically to be a basal cell carcinoma, was excised. Anastomosing lobules of small uniform basaloid (poroid) cells formed small ductular structures lined by eosinophilic cuticles and extended into the superficial reticular dermis. The neoplasm originated from follicular infundibula and was surrounded by a myxoid stroma. Focally, primitive hair bulb and papillae differentiation was present, and some of the ducts were lined by cells suggesting decapitation secretion. The histologic pattern and the common embryologic origin of the folliculosebaceous-apocrine unit support apocrine differentiation of this tumor. The association with the nevoid basal carcinoma syndrome appears to be unique. This case, in addition, demonstrates overlapping features with the infundibulocystic type of basal cell carcinoma commonly seen in the basal cell nevus syndrome.