Arising in Pleomorphic Adenoma

p53 protein immunoexpression was evaluated in 17 invasive carcinomas arising in pleomoqhic adenoma and correlated with the histologic type and tumor grade. Ten tumors had one malignant histologic component: adenocarcinoma NOS (not otherwise specified) (five), undifferentiated carcinoma (two), malignant myoep-ithelioma (one), epithelial-myoepithelial carcinoma (one), and malignant oncocy-toma (one). In the remaining cases, there was a coexistence of areas of adenocarci-noma (seven), adenosquamous (two), epithelial-myoepithelial (two), adenoid cystic (two), undifferentiated carcinoma (one), and lowgrade polymorphous ade-nocarcinoma (one). p53 positivity was found within adenocarcinoma NOS (three) and adenosquamous carcinoma (two) components of four cases. Tumor areas showing loW-grade histology, either mono- or bidifferentiated carcinomas, were always negative in this series, in keeping with previous observations on primary neoplasms of the same histologic type. The benign component of the neoplasms was also found to be consistently negative. The results point to a preferential associ-ation of the p53 gene dysfunction and its protein accumulation with the malignan