osteosarcoma

Osteosarcoma is the most common primary malignant bone tumor, defined by malignant osteoid production by neoplastic cells. It most often affects adolescents and young adults and typically arises in the metaphyses of long bones, especially the distal femur, proximal tibia, and proximal humerus. Patients usually present with localized bone pain and swelling; a pathologic fracture may occur.

Epidemiology and risk factors: The incidence peaks in the second decade of life, with a smaller rise in older adults with Paget disease or previous radiation. It accounts for about 10–20% of primary bone cancers and shows a slight male predominance.

Pathology and subtypes: Conventional osteosarcoma is the most common form, with osteoblastic, chondroblastic, or fibroblastic patterns. Other subtypes include telangiectatic and small cell variants. All demonstrate malignant cells producing osteoid or immature bone.

Diagnosis and staging: Plain radiographs often show mixed lytic and sclerotic destruction with aggressive periosteal reaction, sometimes sunburst calcification or Codman triangle. MRI assesses local extent; CT or MRI of the chest evaluates pulmonary metastases. Definitive diagnosis requires biopsy demonstrating malignant osteoid.

Treatment: Management is multidisciplinary, combining systemic chemotherapy with surgical resection. Neoadjuvant multiagent chemotherapy is commonly given to shrink the tumor and assess chemosensitivity, followed by wide resection with clear margins. Limb-sparing surgery is preferred when feasible; amputation is reserved for cases with inadequate margins or extensive involvement. Radiotherapy has a limited role, usually for palliation or unresectable disease.

Prognosis: Localized disease treated with modern therapy has a 5-year survival around 60–80%, depending on response to chemotherapy and tumor size. Metastatic disease at diagnosis and poor histologic response predict worse outcomes. Histologic tumor necrosis after neoadjuvant therapy is an important prognostic factor.