Carcinoma in basal cell adenoma of the parotid gland.

Malignant transformation of basal cell adenoma (BCA) of the parotid gland is rarely reported, and when occurred, may principally become manifest as a malignant basaloid tumor, i.e. basal cell adenocarcinoma or adenoid cystic carcinoma. We describe herein three cases of non-basaloid carcinoma arising in BCA. The incidence of this malignant tumor was 0.2% of all parotid gland tumors and 4.3% of BCAs in our series. One case was salivary duct carcinoma showing histologic evidence of transition between malignant and benign elements. The remaining two cases were well-encapsulated parotid gland tumors, which were composed of BCA and scattered foci of malignant transformation. Malignant components were adenocarcinoma, not otherwise specified (NOS), and sometimes intermixed with neoplastic myoepithelial cells included BCA cells. These two cases were regarded to be intracapsular carcinoma in BCA. BCA components showed solid, tubular and trabecular arrangements. The patients' prognosis was quite variable among these three cases; the first case died of disease after 27 months, whereas the latter two cases are alive and well for 4 and 10 years after surgery. Ki-67 labeling index indicated that cell proliferative activity was at least five times higher in carcinomas than BCAs. Non-basaloid carcinomas such as salivary duct carcinoma or adenocarcinoma, NOS, do develop in BCAs as in the case of a pleomorphic adenoma with malignant transformation, though the incidence may be extremely rare.