Why is it blue AND squamous? A report of cylindrocarcinoma with squamous differentiation

Summary: Cylindrocarcinoma is an uncommon adnexal carcinoma first described by Wieldman in 1929. It does not harbor distinctive clinical features and can present as a manifestation of Brooke-Spiegler syndrome. Histopathologically, cylindrocarcinoma shares some features in common with its benign analogue (cylindroma) but is recognizable on the basis of malignant features such as nuclear crowding, necrosis, and an elevated mitotic index. Historically, the immunophenotype associated with cylindrocarcinoma has been nonspecific, but SOX10 expression can now be used as a tool to distinguish the spiradenocylindrocarcoma spectrum (and also transformed adenoid cystic carcinoma) from other basaloid carcinomas. Squamous differentiation has been rarely documented within the spiradenocylindrocarcinoma spectrum. In the series of Granter et al. (2000), however, 2/12 tumors (16%) exhibited partially squamous histomorphology. We report a poorly differentiated example of cylindrocarcinoma with marked squamous differentiation that mimicked other types of basaloid carcinoma with cornification, in particular matrical carcinoma. A specific diagnosis was possible on the basis of conventional microscopic features and SOX10 immunopositivity. The literature and differential diagnosis of keratinizing basaloid carcinomas will be reviewed.