Abstract

EWSR1-NR4A3 gene fusion is a well described molecular alteration in extraskeletal myxoid chondrosarcoma and not commonly described in other malignancies. We report a 72-year-old female with an enlarging subcutaneous mass in the mid back. Fifteen years prior, she underwent excision of a lesion in the same location, but for which pathology results were unknown. The new mass was a 1.6 cm relatively well-circumscribed nodule. Histologic sections demonstrated a subcutaneous lobulated solid tumor composed of nests and sheets of spindle, epithelioid and ovoid cells with prominent vasculature. The cells had vesicular to clear cytoplasm, moderate nuclear enlargement, identifiable nucleoli, mild pleomorphism and up to 6 mitoses/10 high power fields. Necrosis was not identified. Immunohistochemically the tumor cells were immunoreactive for pancytokeratin, p63, CD99, and weakly for SMA. Tumor cells were negative for EMA, S100, GFAP, p40, desmin, caldesmon, muscle specific actin, calponin and SOX10. An EWSR1 rearrangement was detected by fluorescence in-situ hybridization (FISH). Based on the H&E morphology, immunohistochemical profile and FISH studies, a diagnosis of myoepithelial carcinoma was rendered. Next generation sequencing revealed an EWSR1-NR4A3 gene fusion. Although the EWSR1-NR4A3 gene fusion has been mainly described in extraskeletal myxoid chondrosarcoma, this diagnosis is not favored based on the clinical presentation, tumor morphology and IHC findings. We present this case to bring awareness that this translocation can be identified in myoepithelial carcinoma and is not exclusive for extraskeletal myxoid chondorsarcoma.

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