True malignant mixed tumor (carcinosarcoma) of the parotid gland. Report of a case with immunohistochemical study.

We present a rare case of parotid gland carcinosarcoma that occurred in an 86-year-old woman. Clinical and histologic data revealed it had developed from a preexisting pleomorphic adenoma. Microscopic examination showed a neoplasm comprised of sarcomatous elements, mainly fibrosarcoma, intermingled with salivary duct-type carcinoma. Sarcomatous cells, excluding those that show chondrosarcomatous differentiation, reacted positively with antibodies directed against vimentin. Carcinomatous cells were positive for epithelial membrane antigen and keratin and negative for myoepithelial markers, which suggest an origin from salivary duct cells. This tumor seemed to consist of two histogenetically different populations of cells without evidence of a common origin from the myoepithelial cell. We also review the literature and discuss the histogenetic origin of true carcinosarcoma of salivary gland.