Myoepithelial carcinoma of soft tissue: a case report.

Myoepithelioma of soft tissue is a recently categorized entity and myoepithelial carcinoma is extremely rare. We describe a case of myoepithelial carcinoma of soft tissue in a 30-year-old male patient, who presented with a painless mass located at the back of left leg involving popliteal fossa that was present since childhood. A wide local excision was performed. The distinct histopathological features included infiltrative margins, cytologically moderate to severely atypical epithelioid/spindled cells with prominent nucleoli, 3-4 mitoses/10HPF, tumor necrosis and lymphovascular invasion. No heterologous elements were identified. The myoepithelial origin was confirmed by positive immunohistochemical staining for S100 protein, epithelial membrane antigen and smooth muscle actin. Mib-1 (Ki-67) proliferation index was 20-25%. These carcinomas have variable clinical presentation and can have an indolent course for several years. Recognition of myoepithelial carcinoma is clinically significant because compared to its benign counterpart, this has increased frequency of local recurrences and metastases that warrants a close clinical follow-up.