Post-chemotherapy neuroblastoma-like differentiation in ewing sarcoma of humerus: Report of a rare case with review of literature

A 21-year patient initially presented with a fracture of the humerus following minor trauma. A bone scan and biopsy were done due to the suspicion of pathological fracture and the biopsy confirmed the diagnosis of Ewing Sarcoma (EWS). Two months after initial presentation, chemotherapy was started and 5 cycles were given over a span of 6 months. Surgical resection of the tumor was then performed. The post-chemotherapy resection specimen, on histological examination, showed the presence of areas of neuroblastoma-like differentiation in otherwise morphologically classic EWS. Cytogenetic analysis by FISH revealed EWSR1 gene rearrangement. Four similar cases have been reported earlier in literature, all in females below 20 years of age. Our case is unique as it is the first case of post-chemotherapy neuroblastoma-like differentiation of EWS in a 21-year male.