Basaloid Tumors: Basal Cell Adenoma and Basal Cell Adenocarcinoma

Basaloid tumors of the salivary gland are among the most diagnostically challenging areas of salivary gland FNA cytopathology. The primary tumors included in this group are basal cell adenoma, basal cell adenocarcinoma, and the solid variant of adenoid cystic carcinoma. In addition, various other salivary gland tumors, such as cellular pleomorphic adenoma, can also exhibit basaloid features and will be considered as differential diagnostic entities within this section. Basal cell adenomas are rare salivary gland tumors comprised of basaloid cells and lacking the chondromyxoid matrix material characteristic of pleomorphic adenomas. In the past, they have been classified as “monomorphic adenomas,” but this nonspecific terminology is to be avoided in favor of the more specific designation recommended by the WHO “basal cell adenoma.” Basal cell adenomas represent 1%–3% of all salivary gland neoplasms, and they arise primarily in older adults, usually in the sixth to seventh decade. A somewhat histologically similar basaloid tumor that occurs in infants is known as sialoblastoma. Over 75% of basal cell adenomas occur in the parotid gland; they are rarely seen in minor salivary glands. There are 3 subtypes of basal cell adenoma: solid, tubulotrabecular, and membranous. Most patients present with a solitary firm nodule between 1 and 3 cm that is slowly enlarging. Occasionally, basal cell adenomas can be cystic.