Evidence of neural differentiation in a case of post-therapy primitive neuroectodermal tumor/Ewing sarcoma of bone

Neural differentiation with the appearance of ganglion-like cells has been reported in untreated primitive neuroectodermal tumor/Ewing sarcoma (PNET/EWS) at peculiar sites, such as the cauda equina, and following treatment. The case is presented here of a 17-year-old girl with a tumor in the iliac bone. An open biopsy was diagnosed as PNET/EWS of the bone. The tumor had the typical morphology of this tumor type and showed diffuse membranous immunoreactivity for CD99, intense immunoreactivity for synaptophysin, and focal immunoreactivity for neuron-specific enolase and S-100 protein. Occasional reactivity for vimentin was evident, while no immunoreactivity for NB84a, Hu, chromogranins A and B, neurofilaments, cytokeratins, and desmin was present. The patient underwent chemotherapy and radiotherapy, followed by right internal hemipelvectomy. The post-treatment residual viable tumor showed a morphologic appearance resembling a neuroblastoma, with immunoreactivity for NB84a, Hu, synaptophysin, and chromogranins A and B, but not for CD99. RTPCR performed on tumor tissue before and after therapy showed the presence of the EWS-FLI1 fusion transcript, type I in both samples. This case of PNET/EWS is unique in the sense of showing the typical fusion transcript associated with this tumor both in the morphologically typical pretherapy tumor and in the sample from the post-therapy specimen showing neuroblastoma-like features.