Abstract
The Ewing family tumors (EFT) of soft tissue represent a spectrum of neoplasms of uncertain histogenesis, arising in soft tissue without bone involvement. They include Extraskeletal Ewing Sarcoma and Primitive Neuroectodermal Tumor. These tumors are morphologically indistinguishable from Ewing sarcoma of the skeletal system. Known to be translocation-associated neoplasms, they share a common non-random translocation leading to the fusion of the EWSR1 gene on the 22q12 region, with one of the many members of the ETS family of transcription factors. Occurring mainly in adolescents and young men under the age of 30, EFT´s may arise virtually anywhere, but are most common in deep soft tissues of the extremities. The purpose of this work is to report a rare case of an EFT arising in the upper arm of a 14-year-old boy, who presented with a painful right arm mass evolving for 6 months, while highlighting the main histological, immunohistochemical and molecular features of this rare condition, along with an original flow chart of a relevant diagnostic approach for differential diagnosis.