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.