title: Ewing's sarcoma/primitive neuroectodermal tumor of the proximal humeral epiphysis.
abstract: Ewing's sarcoma/primitive neuroectodermal tumor (ES/PNET) of bone is a rare childhood tumor most commonly located in the metadiaphysis. In skeletally immature patients, lesions of the epiphysis are rarely malignant, with the most common diagnosis being chondroblastoma. This article presents a case of ES/PNET of the proximal humeral epiphysis in a 12-year-old boy. To the authors' knowledge, this is the first reported case of epiphyseal ES/PNET confirmed with molecular testing. Radiographs of the patient's painful shoulder showed a well-defined lytic lesion within the humeral epiphysis. Magnetic resonance imaging suggested a chondroid tumor with surrounding edema. Based on the imaging characteristics, the patient's age, and the lesion's location, a preliminary diagnosis of chondroblastoma was made. A trochar biopsy of the lesion demonstrated a small, round, blue cell tumor on frozen section. Subsequently, immunohistochemical staining was uniformly positive in a membrane pattern for CD99, and molecular diagnostic testing demonstrated a EWSR1/FLI1 fusion transcript, confirming the pathologic diagnosis of ES/PNET. Although metadiaphyseal locations for ES/PNET are most common, this case adds to previously reported cases of epiphyseal ES/PNET, suggesting that the diagnosis be considered for pediatric epiphyseal tumors. This case also demonstrates why following rigorous oncologic treatment algorithms by obtaining a limited trochar biopsy, even in the case of a confident radiographic diagnosis, is critically important; the biopsy results can lead to a major change in treatment and avoid contamination of a larger area of soft tissue and bone.
authors.affiliation: Department of Orthopaedic Surgery, University of Arizona, Tucson, USA.
authors.forename: Parisa
authors.initials: P
authors.lastname: Morris
authors.forename: Paul S
authors.initials: PS
authors.lastname: Dickman
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Seidel
mesh_terms: D001859:Bone Neoplasms / Q000175:diagnosis*; D002648:Child; D004838:Epiphyses / Q000473:pathology*; D006801:Humans; D058430:Humeral Head / Q000473:pathology*; D008297:Male; D018241:Neuroectodermal Tumors, Primitive, Peripheral / Q000175:diagnosis*; D012512:Sarcoma, Ewing / Q000175:diagnosis*