Basaloid squamous carcinoma of the head and neck. Immunohistochemical comparison with adenoid cystic carcinoma and squamous cell carcinoma.

Basaloid squamous carcinoma (BSC) is a rare distinct variant of squamous cell carcinoma of the head and neck region. This entity may commonly pose diagnostic difficulties, especially on small biopsy material. We report the clinicopathological characteristics of 12 new cases and compare their immunohistochemical features with those of solid adenoid cystic carcinomas and conventional squamous cell carcinomas. Our results show that neoplastic BSCs and squamous cell carcinomas do not react to vimentin and S100 protein, while adenoid cystic carcinomas manifest both. The BSCs, however, are S100 protein-positive in intratumoral dendritic Langerhans' cells that are lacking in squamous cell and adenoid cystic carcinomas. Our findings indicate that the immunohistochemical differences between BSC and adenoid cystic carcinoma could assist in their differential diagnosis.