Intraosseous epithelioid malignant peripheral nerve sheath tumor of the phalanx - Case report

We report the first case of intraosseous epithelioid malignant peripheral n erve sheath tumor (MPNST) occurring in the phalanx. The patient was a 50-ye ar-old Japanese man with an intramedullary lytic lesion of the proximal pha lanx. Microscopically, the tumor was composed of epithelioid cells or polyg onal cells, forming large cell nests with central necrosis. Most tumor cell s were diffusely and strongly immunopositive for S-100 protein and vimentin , and negative for cytokeratin, epithelial membrane antigen, carcinoembryon ic antigen, alpha-smooth muscle actin, and HMB-45. Laminin-positive materia l was discontinuously demonstrated between the individual tumor cells. Elec tron microscopy showed prominent external lamina. Our case indicated that l aminin is useful for differentiating epithelioid MPNST from metastatic carc inoma and malignant melanoma.