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Case Reports

Abstract

Mesenchymal tumors may display morphologic and immunohistochemical overlap with melanocytic tumors, creating the potential for misdiagnosis. We report a 62-year-old woman who presented with a recurrent dermal and subcutaneous tumor over the Achilles tendon 15 years following complete excision. Both the primary and the recurrent tumors were characterized by nests and sheets of epithelioid and spindle cells with eosinophilic cytoplasm and uniform ovoid nuclei. The tumor was positive for S100, SOX10, HMB45, cathepsin K, and p63 (weak), while negative for Melan-A, MiTF, smooth muscle actin, and desmin. Fusion panel analysis of the recurrent tumor revealed a NONO::TFE3 fusion which has been recently reported in two similar cases. Our case represents the first report of recurrent NONO::TFE3 cutaneous epithelioid and spindle cell tumor after a prolonged disease-free interval without evidence of high-grade transformation or distant metastasis. Our findings support its classification as a cutaneous mesenchymal neoplasm of intermediate malignancy.