Basal cell adenoma in the parotid: a bizarre myoepithelial-derived stroma rich variant.

Basal cell adenoma (BCA) is a specific entity that lacks the myxochondroid stromal component of a pleomorphic adenoma. There are six histopathological types of BCA: solid, tubular, trabecular, membranous, cribriform, and myoepithelial-derived stroma rich. Myoepithelial-derived stroma rich variant is so rare, especially with cellular atypia. Herin we describe a rare case of BCA arising in the parotid on a 25-year-old man. A well-demarcated nodule arising in the parotid that was composed of basaloid cells, forming small duct-like or tubular structures containing basement membrane-like material, as well as highly cellular elongated cells with hyperchromatic, enlarged, pleomorphic, and bizarre nuclei. Immunohistochemically, S100 protein and p63 highlighted the basal aspect of the peripheral epithelial cells and peripheral spindle and bizarre cells, while CK7 expressed on the luminal cells. We made a diagnosis of "basal cell adenoma, myoepithelial-derived stroma rich variant, with bizarre myoepithelial proliferation". The differential diagnosis includes cellular pleomorphic adenoma, basal cell adenocarcinoma, and carcinoma ex pleomorphic adenoma. After follow-up for 3 years, there was no evidence of recurrence. Further pathological characteristics of this disease are discussed.