A 19 year old woman presented with an enlarging mass in the anterior abdominal wall. A well-circumscribed intramuscular 8 cm mass was excised.

Pathologic Findings The lesion consists of variably sized nests or trabeculae, composed of large polygonal or epithelioid cells. The tumor cells have copious palely eosinophilic granular or clear cytoplasm and mainly vesicular nuclei with variably prominent nucleoli. There is focally striking nuclear pleomorphism, but mitoses are hard to find and there is no necrosis. The nests of tumor cells are separated by a prominent network of branching thin-walled vascular channels. Immunohistochemical stains show multifocal positivity for desmin and Melan-A, along with diffuse positivity for HMB45, while SMA is negative. There is diffuse nuclear positivity for TFE3.

PEComa (of uncertain biologic potential)