Rare variants of head and neck squamous cell carcinoma -differential immunohistochemical profiles.

We aimed to immunohistochemically characterize the pattern of expression of epithelial markers in rare head and neck squamous cell carcinoma (HNSCC) variants: carcinoma cuniculatum (CC) and adenosquamous carcinoma (ASC). We also present an additional variant of HNSCC with concomitant basaloid and squamous components that has overlapping morphological features with odontogenic and non-odontogenic tumors, which we termed basalo-squamous carcinoma (BSC). The selected markers included CK5/6, p40, CK19, BerEP4, p16 and SOX10. All tumors were CK5/6 and p40 positive. CK19 and BerEP4 were positive in BSC and focally in ASC but negative in CC. p16 was positive in 3 (60%) of the CCs, focally positive in ASC and negative in BSC. SOX10 was negative in all three variants. Our results highlight the plasticity of the lining epithelium revealing differential profiles of immuno-expression of the selected molecular markers, possibly reflecting their diverse histopathogenesis.