Myopericytoma of soft tissue (thigh) ★

The recent recognition of concept of perivascular myoid cell (PMC) phenotype and perivascular epithelioid cell (PEC) phenotype has changed the concept of angiogenic tumors, in particular “hemangioperycytoma” (HPC)-like tumors. The PMC concept has yielded myopericytoma, myofibroma, myofibromatosis, angioleiomyoma, and glomus tumors, while the PEC concept that shows melanocytic lineage has given rise to PEComa, clear cell sugar tumors, angiomyolipoma, and lymphangiomyomatosis. Here, the author reports a case of myopericytoma of soft tissue (thigh) occurring in a 47-year-old man. The patient had noticed the thigh tumor 4 years before, and was admitted. The tumor was located in subcutaneous tissue, was encapsulated, and measured 4 × 3 × 3 cm. Total excision was performed. Grossly, the tumor is a soft reddish encapsulated tumor with very well demarcation. Histologically, the tumor showed typical HPC-like features with focal nodular proliferation of HPC-like tumor cells. Immunohistochemically, the vasculatures were positive for vimentin, CD31, CD34, and factor VIII-related antigen. In contrast, the HPC-like tumor cells were positive for vimentin, α-smooth muscle antigen, h-caldesmon, bcl-2, and factor XIIIa, but negative for cytokeratins, desmin, CD31, CD34, factor VIII-related antigen, S100 protein, melanosome, CD99, and KIT. Ki-67 labeling was 15%, and p53 was mildly positive. The overall features were those of myopericytoma. The patient is now alive without recurrence 5 years after the operation. A brief literature review and differential diagnosis were made.