Mixed tumors, myoepitheliomas, and oncocytomas of the soft tissues are likely members of the same family: A clinicopathologic and ultrastructural study

Four diagnostically unusual soft tissue tumors are presented. All lesions w ere of consistent size and long duration. Histologically, one lesion was an alogous to mixed tumors of the usual sites (i.e., salivary glands), one les ion was totally spindled, and the two other lesions both had oncocytic appe arances (epithelioid and spindle biphasic pattern in a case, purely epithel ioid in the other). Immunohistochemically, the mixed tumor was positive for vimentin, cytokeratins, S-100 protein, and focally for EMA. The purely spi ndled tumor exhibited immunoreactivity for vimentin, actins, S-100 protein, EMA (focally), and GFAP. The oncocytic biphasic tumor was positive for mit ochondrial antigen, vimentin, and actins. The purely epithelioid oncocytic neoplasm was immunoreactive only for mitochondrial antigen and vimentin. Ul trastructurally, in the epithelial-like portion of the first (mixed) tumor, peripheral arrays of contractile filaments were detected along with well-d eveloped desmosomes. In the second (spindled) case, peripheral contractile filaments and attenuated desmosomes were also seen. In the third case, a hu ge number of mitochondria, some desmosomes, and actin-type microfilaments w ere found. In the fourth case, desmosomes and punctate subplasmalemmal dens ities, in addition to numerous mitochondria, were documented. In all cases an external basal lamina were present, which was discontinuous in the first three cases and almost continuous in the fourth. These tumors were respect ively designated as mixed tumor, myoepithelioma of the classic type, myoepi thelioma of oncocytic type with biphasic cell architecture, and true oncocy toma. So far, all tumors have followed benign clinical courses (median foll ow up: 12 months). Comparisons with similar tumors of other sites are drawn , and suggestions for considering all of them as members of the same myoepi thelial-derived tumor family are given.