Inclusion Criteria:  Patients with Ewing's Sarcoma and osteosarcoma with established diagnosis; Patients with age ≥ 2 years; Minimum follow-up duration of 2 years; Medical records, complete blood work and instrumental examinations; Regular follow-up.  Exclusion Criteria:  Patients with Ewing's sarcoma or osteosarcoma who have received medical treatment (surgery radiotherapy or chemotherapy) in other institutions prior to admission to the Rizzoli Orthopaedic Institute.