Abstract

The terms "malignant mixed tumor" and "carcinoma arising in pleomorphic adenoma" have been used interchangeably. However, they are theoretically quite different. The term carcinoma arising in pleomorphic adenoma refers to an epithelial malignancy in which remnants of benign pleomorphic adenoma (mixed tumor) matrix can be identified. And metastasis contains only the carcinomatous component. The important microscopic findings are 1) destructive infiltrative growth 2) necrosis and extensive hyalinization 3) frequent mitosis and pleomorphism 4) dystrophic calcification 5) anigo and perineural invasion, and 6) metastasis. Recently we have experienced four cases of major salivary gland carcinomas that showed residual foci of benign pleomorphic adenoma. Detailed histological examination confirmed that these tumors fit the criteria of "carcinoma arising in pleomorphic adenoma". The tumors occurred most commonly in parotid(3 cases), in males(3 cases) and over the age of 60 years(4 cases). The malignant part of the tumors was comprised of poorly differentiated adenocarcinoma in three, and squamous cell carcinoma in one case. One patient died of brain metastasis.