[Epithelioid variant of malignant peripheral nerve sheath tumor]

Epithelioid variant of malignant peripheral nerve sheath tumor arising from deep soft tissue is an uncommon neoplasm, histopathologic features of which are usually not homogenous. The aim of this study was designed to investigate the relation between morphologic features and prognosis of the tumor. Twelve cases were studied with light microscopy, immunohistochemistry, and 7 cases were studied with electron microscopy. Histologically, there were three patterns: purely epithelioid (5 cases), mixed with areas of spindle cells (5 cases) and ossifying (2 cases). The results showed S-100 protein positivity and multiple cytoskeletal heterogeneity that included: (1) neuronal differentiation which indicated expression for NSE and neurofilament, and ganglion cell; (2) epithelial differentiation which revealed reactivity for Keratin, and desmosomes and tonofilament-like bundles in ultrastructural findings; (3) mesenchymal differentiation which manifested reactivity for vimentin, osteoid metaplasia, and rhabdoid phenotype. The present study indicates that the relation between the heterogeneity and the aggressiveness of the tumors is synchronous. Three of the patients with prominent heterogeniety died with clinical evidence of lung metastases within seven months to four years after diagnosis.