Carcinomas ex pleomorphic adenoma and malignant mixed tumors. Histomorphologic indexes.

Clinical and pathologic differences exist between the several neoplasms encompassed by the term malignant mixed tumors of salivary glands. The majority of the neoplasms are carcinomas ex pleomorphic adenoma. True malignant mixed tumors (carcinosarcomas) are rare, and even more rare are the benign metastasizing mixed tumors. This study of 40 malignant mixed tumors indicates that two previously unreported variables, measured invasion in millimeters and histologic subclassifications of the malignant neoplasm, are valuable guides to prognosis and biologic behavior. All patients whose malignant neoplasm extended for more than 8 mm beyond residual capsule or benign residual tumor died of their disease. The extent of invasion also correlated with perineurial invasion, involvement of bone, and metastases to lymph nodes. Histologic subclassification points out that there is no prototypical carcinoma ex pleomorphic adenoma and that high- and low-grade carcinomas can be found. Only one of the patients with low-grade (terminal duct) carcinomas died of his disease during follow-up periods extending to over 20 years.