Congenital Peripheral Primitive Neuroectodermal Tumor (pPNET)/Ewing's Sarcoma of the Upper Limb in a Neonate: A Rare Case Report

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Background: Ewing’s sarcoma (EWS)/peripheral primitive neuroectodermal tumor (pPNET) is a rare, aggressive small‑round‑cell malignancy primarily of children and adolescents; congenital presentations are exceptional. We report a neonate with congenital pPNET of the arm. Case presentation: A 24‑day‑old full‑term female presented with a progressively enlarging left‑arm swelling present since birth. Birth and maternal histories were unremarkable; no family history of genetic disease. Clinical findings: Examination revealed a 6 × 6 cm soft, immobile posterolateral arm mass. Laboratory values were within normal limits. Diagnostic assessment: Ultrasound showed a hypoechoic lobulated intermuscular lesion. MRI demonstrated a well‑circumscribed T1 hypointense, T2/STIR hyperintense ovoid mass abutting but not invading adjacent structures. FNAC revealed sheets of small round blue cells. Excisional biopsy showed uniform small round cells; immunohistochemistry was CD99 and vimentin positive, desmin, myogenin, synaptophysin, S‑100, EMA, and LCA negative. Cytogenetic/molecular testing was not performed due to resource constraints. Therapeutic intervention: Radical surgical resection followed by four cycles of cisplatin and cyclophosphamide at 3‑week intervals. Follow‑up and outcomes: Immediate postoperative imaging showed no metastasis; postoperative course was uneventful. Patient lost to follow‑up after three months. Conclusion: Congenital pPNET/EWS is extremely rare and aggressive. Diagnosis relies on histopathology and IHC when molecular tests are unavailable. Early recognition and multimodal therapy are critical, but prognosis in neonates remains guarded.