Abstract

Primary cutaneous perivascular epithelioid cell tumors (PEComas) are exceedingly rare, representing only 8% of all PEComas, with only 65 cases reported to date. We report a case of primary cutaneous PEComa in an 80-year-old male. The lesion was erythematous, slow-growing, and asymptomatic, measuring 1.2 cm in greatest dimension, and was located on the patient’s right ring finger. Clinical differential diagnoses included a digital myxoid cyst and a vascular tumor. The patient underwent excision and histopathology revealed a well-circumscribed multinodular dermal tumor composed of nests of monotonous epithelioid to spindled cells with pale eosinophilic granular to clear cytoplasm. Prominent vascularity and hemorrhage were present, with the tumor cells arranged around the irregular vascular channels. Moderate nuclear atypia was present. The tumor cells were positive for SOX10 and S100, and negative for HMB-45, Melan-A, SMA, desmin, CD34, and CD31. Next generation sequencing revealed the NONO-TFE3 fusion that is characteristic of PEComas, clinching the diagnosis. PEComas are known to express myoid and melanocytic markers, with the most reliable melanocytic markers being MiTF and HMB-45, and the most reliable muscle markers being SMA and desmin. SOX10 and S100 are typically not expressed, with S100 positivity seen in about a third of extracutaneous lesions. The NONO-TFE3 fusion is very rare and has never been reported in prior primary cutaneous PEComas. Most tumors harboring the fusion represent MiT family translocation renal cell carcinomas, and rare extrarenal PEComas, including three from the sinonasal tract, two from the orbits, and one from the prostate. PEComas can be very hard to differentiate from melanoma, considering the morphologic and immunophenotypic overlap. Making the right diagnosis is crucial because of treatment implications. Our case highlights the importance of molecular findings in the diagnosis of PEComas.

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