Salivary gland carcinosarcoma: immunohistochemical, molecular genetic and electron microscopic findings.

Salivary gland carcinosarcoma, or true malignant mixed tumor, is a very rare and extremely aggressive neoplasm. The clonality and clonal origin of this tumor are discussed controversially. We report a carcinosarcoma of the left parotid gland in a patient who subsequently died of cutaneous, lymphatic and pulmonary metastases. Immunohistochemical staining, electron micrograph analysis, loss of heterozygosity (LOH) analysis and sequence analysis were performed on this tumor with an adenocarcinomatous and a predominant spindle cell-like component. While smooth muscle actin was undetectable by immunohistochemistry, cytoplasmatic myoepithelial structures could be detected by electron microscopy. LOH analysis at 12 genomic locations detected complete deletion of one allele at 17p13.1, 17q21. 3, and 18q21.3 indicating allelic loss in both components of the tumor. Double strand sequencing of the remaining allele of the p53 tumor suppressor gene revealed a wild-type allele. Based on our results, we favor the hypothesis of monoclonal origin of this salivary gland carcinosarcoma with a common stem cell that could be the myoepithelial cell and an inactivated tumor suppressor gene on chromosome 17 other than p53.