Syringocystadenocarcinoma papilliferum with transition to areas of squamous differentiation: a case report and review of the literature.

Syringocystadenocarcinoma papilliferum (SCACP) is an exceedingly rare cutaneous adnexal neoplasm, which is typically located in the head and neck, and perianal area. Very few cases have been reported in the literature. Here, we report a case of SCACP with evident transition to squamous differentiation. A 75-year-old white woman presented with 1-year history of a solitary tender nodule in the left upper arm. Physical examination revealed a single, 1.5 × 1.1-cm, erythematous ulcerated nodule within a background of red patch. Biopsy showed an adnexal carcinoma connected to the epidermis and composed of cystic papillary projections admixed with solid basaloid areas with marked cytologic atypia. The basaloid tumor cells appeared to blend with the squamous component that demonstrated ductal formation, which was highlighted by carcinoembryonic antigen. Tumor cells were reactive for both cytokeratins 5/6 and 7. This case represents SCACP arising from syringocystadenoma papilliferum in the upper arm, with distinct transition to areas of squamous differentiation.