Ewing-Like Sarcoma: A Case of a Primary Cutaneous Primitive Neuroectodermal Tumor With Atypical Immunohistochemistry and Lack of Fusion Oncogene Detection.

We present a 25-year-old male patient with a primary cutaneous primitive neuroectodermal tumor (cPNET) with unusual immunohistochemistry and lack of fusion oncogene generation. The lesion expressed CD99 and WT-1, and the histological features were consistent with cPNET. Differential diagnoses such as rhabdomyosarcoma, desmoplastic small round blue cell tumor, hematolymphoid neoplasm, neuroblastoma, and CIC-DUX round cell sarcoma were ruled out based on immunohistochemistry, genetic studies, and histology. Previous cPNET cases have been published detailing abnormal immunochemistry and genetic expression. However, to our knowledge, fusion oncogene negativity in cPNET tumors has only been reported in one other published case series. These reports, including this study, reinforce the fact that a high index of suspicion should be used when diagnosing these tumors, regardless of immunohistochemical and genetic variability. This case highlights that the typical genetic and immunohistochemical features of cPNET may be more variable than previously thought. Future studies are needed to better understand these variations of cPNET.