Myoepitheliomas in inbred laboratory mice

Myoepitheliomas are subcutaneous tumors that arise from myoepithelial cells of various exocrine glands. In a retrospective study of 142 tumors observed over a period of 3 years, myoepitheliomas occurred spontaneously in A/HeJ, A/J, BALB/cJ, BALB/cByJ, LLC.A/Ckc, and NOD/Lt inbred strains of mice. Tumors presented primarily in the subcutaneous tissues of the ventral neck (74% of the myoepitheliomas evaluated) but were observed in several other subcutaneous locations, including the head, perineum, and ventral abdomen. These areas were adjacent to salivary, mammary, clitoral, preputial, and Harderian glands. Forty myoepitheliomas were tested by the avidin-biotin complex technique with a panel of antisera specific for mouse keratins, intermediate filaments, and other cytoskeletal proteins to determine the cell type from which this neoplasm originated. Antibodies directed against the specific mouse keratins K5, K6, and K14, and a broadly cross-reactive cytokeratin antibody stained acinar and ductal myoepithelial cells in normal mammary, salivary, and Harderian glands, and neoplastic cells in all cases. Antisera directed against a smooth muscle actin (anti-alpha-sm-1) stained acinar myoepithelial cells of the glands and vascular smooth muscle but neither ductular myoepithelial cells nor tumor cells. This supports the notion that these tumors originate from extraglandular ductular myoepithelial cells. Southern blots, prepared from DNA extracted from nine myoepitheliomas, did not show restriction fragment length polymorphisms when mouse mammary tumor virus (MMTV) cDNA or Int-1 genomic DNA probes were used; this implies that a retrovirus is not the etiologic agent.