True malignant mixed tumor of the submandibular gland.

A case of true malignant mixed tumor of the submandibular gland is reported. The submandibular tumor, occurring in a 52-year-old man, started to grow rapidly after a long history without any change in size. Surgical resection was carried out and the resected tumor measured 5.5 cm with a cut surface showing mixed solid structures. Microscopically, the tumor had both carcinomatous and sarcomatous elements, the former consisting of poorly differentiated adenocarcinoma with squamous cell differentiation and the latter consisting of osteosarcoma with chondrosarcomatous and fibrosarcomatous elements. A remnant of benign pleomorphic adenoma could also be identified. Immunohistochemical study demonstrated keratin and epithelial membrane antigen in the carcinoma cells and vimentin in all elements of the osteosarcoma. It is assumed from these clinical and histological findings that the tumor had transformed from a pre-existing benign pleomorphic adenoma.