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* True malignant mixed tumors (carcinosarcomas) of salivary gland origin are exceedingly rare and demonstrate malignant epithelial and stromal components. We report a case of parotid gland carcinosarcoma that showed squamous cell carcinoma and malignant fibrous hystiocytoma without clinical or histologic evidence of a preexisting pleomorphic adenoma. This tumor consisted of 2 histologically different populations of cells without evidence of a common origin from the myoepithelial cell, which is the putative precursor cell of pleomorphic adenoma and its derived carcinosarcoma. In addition to supplementing the literature, this case report includes cytohistologic and immunohistochemical analyses that provide further insights into the variable histogenesis of this neoplasm and the distinction between de novo carcinosarcoma and carcinosarcoma originating from pleomorphic adenoma.
(Arch Pathol Lab Med. 1998;122:743-746)
Malignant mixed tumors comprise 3 different clinicopathologic entities: (1) carcinoma arising in a benign mixed tumor (carcinoma ex pleomorphic adenoma), (2) carcinosarcoma or true malignant mixed tumor, and (3) metastasizing mixed tumor.1 Carcinoma ex pleomorphic adenoma is a benign mixed tumor (pleomorphic adenoma) in which a secondary malignant neoplasm, a carcinoma, arises. This tumor accounts for well over 95% of all malignant mixed tumors.2-4 Carcinosarcoma or true malignant mixed tumor is a tumor composed of both carcinomatous and sarcomatous elements, and both elements are capable of metastasis. This type of mixed malignant tumor is rare, and fewer than 60 cases have been reported. Metastasizing mixed tumor is a controversial entity in which both the primary salivary gland tumor and its metastatic lesions are composed of typical benign-appearing mixed tumor. Just over 25 cases have been reported in the literature.2,5
We report another case of the rare true malignant mixed tumor (carcinosarcoma) of the parotid gland and present the results of immunohistochemical and cytohistologic studies. Implications of these findings on the histogenesis and origin of salivary gland carcinosarcomas are discussed, and the literature is reviewed.
REPORT OF A CASE
An 80-year-old man had a history of rapid right parotid gland enlargement over a period of 2 months. Initially, chronic sialoadenitis was suspected, and he was treated with a course of antibiotics without improvement. He returned 1 month later with significantly greater gland enlargement. A sialogram was nondiagnostic. A computed tomographic scan showed a homogeneously enhancing mass in the right parotid gland measuring...