14.2Epidemiology

•Second most common malignant bone tumor in childhood and sixth most frequent malignant bone tumor

•Annual incidence is 2.7 patients per million children younger than 15 years old (USA)

•Male to female ratio is 1.5:1

•Eighty percent of tumors occur in patients younger than 20 years of age

•Fifty percent of the tumors occur in the second decade of life

•The mean age at diagnosis is 15 years

•More common in the white than in the black population

14.3Localization

•Mainly lower extremities involved, and less frequently in the upper extremities

•Pelvis

•Chest wall

•Less common in the spine or paravertebral region

•Less common in head and neck

14.4Pathogenesis

•Not commonly associated with preceding irradiation therapy in contrast to osteosarcoma

•Not associated with familiar tumor syndromes

•Originating from a precursor cell with the potential for neuroectodermal differentiation, based on ultrastructure, immunohistochemistry, and genetics

14.5 Genetics

• In approximately 95% of patients, there is a reciprocal translocation of the EWS gene on chromosome 22q12 with one of the genes of the FLI oncogene family. The FLII gene, on chromosome 11q24, or the ERG gene, on chromosome 21q22, belong to the latter family

14.6 Pathology

Classification in ES and PNET is controversial and based on subjective and semiquantitative analysis of the grade of neural differentiation