ULTRASTRUCTURAL DISTINCTION OF BASALOID-SQUAMOUS CARCINOMA AND ADENOID CYSTIC CARCINOMA

Basaloid-squamous carcinoma is a unique and infrequent variant of squa mous cell carcinoma with a predilection for occurring in the upper aer odigestive tract. The cardinal diagnostic criteria are the presence of basaloid cells arranged in lobules or cords and a squamous component. Another feature that distinguishes basaloid-squamous carcinoma from c onventional squamous cell carcinoma is the development of multiple foc i of amorphous, eosinophilic, or mucinous materials among the basaloid tumor cells. It is this feature in basaloid-squamous carcinoma that c auses confusion with adenoid cystic carcinoma, especially the solid va riant of adenoid cystic carcinoma. To clarify the distinctive features of these two types of tumors, the ultrastructural findings in three b asaloid-squamous carcinomas from the head and neck region were compare d with three adenoid cystic carcinomas, one from the head and neck reg ion and one each from trachea and bronchus. Widened intercellular spac es, tonofilaments, and replicated basal lamina were present in both ty pes of tumor. However, the ultrastructural features of glandular diffe rentiation were present only in adenoid cystic carcinoma, whereas the ultrastructural features of squamous cell differentiation were present only in basaloid-squamous carcinoma. The distinction between basaloid -squamous carcinoma and adenoid cystic carcinoma is important since ba saloid-squamous carcinoma is a clinically aggressive, high-grade form of squamous cell carcinoma, generally with a worse prognosis than aden oid cystic carcinoma.