Cutaneous Syncytial Myoepithelioma: A Nondescript Skin Tumor With Serious Diagnostic Pitfalls

Cutaneous syncytial myoepithelioma (CSM) is a rare tumor with a nondescript clinical presentation in the skin. It represents a relatively uncommon diagnostic entity with approximately 50 examples in the literature to date. We present a 36-year-old man with a new, tender 3-mm firm pink papule on the left bicep, in which a superficial shave technique produced a diagnostic challenge. CSM often poses a diagnostic quandary given shared histomorphological and immunohistochemical attributes with superficial mesenchymal or neurocristic tumors, namely, melanocytic proliferations, fibrous histiocytoma, and epithelioid sarcoma. The molecular profile of CSM may reveal EWSR1 or FUS gene rearrangement, but as we showcase, the diagnosis remains possible in the absence of this oncogenic fusion. Ultimately, there are pitfalls to avoid to correctly distinguish this benign myoepithelial lesion from more biologically aggressive neoplasia.