Inclusion Criteria:  Osteosarcoma diagnosed at the Pathological Anatomy of the Rizzoli Orthopaedic Institute in Bologna; Minimum 2-year follow-up period; Medical records, complete blood work and instrumental examinations, regular follow-up; Patients with age ≥ 2 years;  Exclusion Criteria:  Patients with osteosarcoma who have received medical treatment (surgery, radiotherapy or chemotherapy) in other hospitals prior to admission to our Institute