DOI: https://doi.org/10.36347/sjmcr.2026.v14i11.031

Pages: 2543-2547

Epithelioid malignant peripheral nerve sheath tumour (EMPNST) is an uncommon variant of MPNST defined by an epithelioid cytomorphology together with diffuse expression of S100 protein and SOX10. It is exceptional in the sinonasal tract, where its morphological and immunophenotypic resemblance to mucosal melanoma, a far commoner tumour at this site carrying the same neural-crest markers, makes it one of the genuine diagnostic traps of head and neck pathology. We report a 56-year-old man who presented with a recurrent nasal mass extending to the nasal floor, having been lost to follow-up before re-presenting with recurrence. The excision specimen showed a high-grade malignant proliferation of spindle and epithelioid cells arranged in short intersecting fascicles and sheets, with marked atypia, vesicular nuclei, prominent nucleoli, brisk mitotic activity and a Ki-67 index near 50%, without necrosis. The tumour expressed S100 with diffuse SOX10 positivity, whereas melanocytic markers (HMB45, Melan-A), cytokeratins, EMA, muscle markers (desmin, h-caldesmon) and neuroendocrine markers were all negative. The absence of melanocytic-marker expression, the fascicular–epithelioid architecture and the lack of any autonomous melanocytic proliferation favoured EMPNST. This case underlines that S100 and SOX10 positivity, however diffuse, cannot by itself separate EMPNST from melanoma, and that the diagnosis rests on integrated morphological, immunophenotypic and clinicopathological reasoning.