Abstract

Cutaneous syncytial myoepithelioma (CSM) is a distinct type of myoepithelial neoplasm that exhibits a unique morphology. It can affect individuals of various ages, ranging from 2 months to 74 years, with a male:female ratio of 2.5:1. Most commonly these tumors are found on the extremities (74%). In the skin and soft tissues, myoepithelial neoplasms are classified as benign mixed tumor/chondroid syringoma, myoepithelioma, and myoepithelial carcinoma. They display a wide range of architectural, cytological and immunophenotypic characteristics within and between different tumors. We present an uncommon variant of myoepithelioma in a 17-year-old female.

Our patient presented with a nodule on shoulder, measuring around 1 cm. The lesion was clinically thought to be pyogenic granuloma, and was treated with excision. Histopathological examination demonstrated well-circumscribed and unencapsulated sheet of cytologically bland, ovoid tumor cells with pale eosinophilic syncytial cytoplasm. The cells were strongly positive for S–100, EMA and SMA and negative for p63, confirming a diagnosis of myoepithelioma.

Typically, myoepithelial tumors express keratin, EMA, S100, and GFAP. Staining for p63, SMA, and calponin varies. However, the syncytial variant consistently demonstrates positivity for EMA and S-100, and is mostly negative for keratin. The absence of significant keratin staining can pose diagnostic challenges. The main differential diagnoses include epithelioid benign fibrous histiocytoma, juvenile xanthogranuloma, melanocytic lesions, and, to a lesser extent, epithelioid sarcoma.

To summarize, CSM is a distinctive subtype of myoepithelial neoplasm, which behaves in a benign manner and familiarity with this neoplasm is necessary to avoid misdiagnosis.