Diagnostic pitfalls in syringocystadenocarcinoma papilliferum: case report and review of the literature.

We report the first case, to our knowledge, of syringocystadenocarcinoma papilliferum with p63-verified squamous differentiation and extensive dermal invasion accompanying in situ components. An 86-year-old woman presented with a neoplasm on the neck, and the intralesional heterogeneity typical of these neoplasms led to an initial diagnosis on needle biopsy favoring squamous cell carcinoma. Excision illustrated diverse morphology, raising a broad differential diagnosis, including more common extracutaneous malignancies, such as breast, gastrointestinal, and ovarian primary tumors. Fortuitous sectioning revealed a focal connection to the skin surface with evidence of apocrine differentiation allowing final diagnosis as syringocystadenocarcinoma papilliferum. Our literature review shows the histologic and immunohistochemical features of syringocystadenocarcinoma papilliferum are not well defined outside of their clear morphologic overlap with syringocystadenoma papilliferum. We describe our findings and diagnostic pitfalls to help pathologists encountering this unusual apocrine neoplasm.