CD99 and peripheral primitive neuroectodermal tumor: The differential diagnosis of pPNET of the orbit includes other small blue round cell tumors which include rhabdomyosarcoma (Actin+, Vimentin+, Desmin +, S-100-ve), Ewing's sarcoma (PGP9.5+, MIC-2+), lymphoma (LCA+, CD45+/CD20+/CD3+), neuroblastoma (PGP9.5+, MIC-2 -ve) and metastatic retinoblastoma to orbit (NSE+, GFAP+).[2–4] Peripheral primitive neuroectodermal tumors are rare lesions that form part of the Ewing family of tumors, which includes osseous and extraosseous Ewing's sarcoma.