Myxofibrosarcoma-Like Spindle Cell Squamous Cell Carcinoma of the Scalp: A Rare Mimic

We report a challenging case of a man in his mid-70s diagnosed with a myxofibrosarcoma-like spindle cell squamous cell carcinoma (ML-SCC) on the scalp. This rare tumor shares cytologic features with spindle cell squamous cell carcinoma (SCC) with myxoid characteristics but also exhibits architectural elements typical of myxofibrosarcoma, making it nearly indistinguishable by routine light microscopic evaluation. Myxoid spindle cell carcinomas are exceptionally rare, and only one case of ML-SCC has been previously documented in the peer-reviewed medical literature. In our case, the tumor initially presented as an ulcerated lesion with intraepidermal keratinocytic atypia and scattered dermal spindle cells embedded in a myxoid stroma. A deeper biopsy revealed a spindle cell neoplasm with myxoid stroma and curvilinear vessels, features typically seen in myxofibrosarcoma. Immunohistochemical (IHC) staining demonstrated positivity of the spindle cells for p40 and CK5/6, confirming the diagnosis of ML-SCC. This case highlights an unusual morphologic variant of SCC and underscores the importance of IHC evaluation of myxoid spindle cell lesion with markers of epithelial differentiation.