Malignant, osteoid and bone-forming tumor arising from osteoblasts located in the periosteum.- Most common primary bone malignancy

- Bimodal distribution→ Primary osteosarcoma: puberty/adolescence→ Secondary osteosarcoma: advanced age- Males > females

Symptoms:- Pain (progressive, worsens at night and with activity)- Swelling after trauma to the bone - Limping and decreased range of motion- B symptoms

Localization: metaphyses of long bones (particularly distal femur and proximal tibia)

Diagnostics:- X-ray: → Signs of osteolysis adjacent to osteosclerosis (moth eaten appearance)→ Sunburst appearance of lytic bone lesions and/or codman triangles- MRI: assesses involvement of soft tissue, evaluation in cases of unclear radiographic findings- Biopsy: Osteosarcomas always feature woven bone matrix → distinction from chondrosarcomas and fibrosarcomas- Laboratory: ↑ alkaline phosphatase, ↑ LDH, ↑ ESR

Treatment:- Definitive resection + neoadjuvant and adjuvant polychemotherapy (e.g., combination of methotrexate, doxorubicin, cisplatin, and ifosfamide)