Define Osteosarcoma. Describe its clinical features, investigations, management and prognosis.

Definition & Epidemiology

Osteosarcoma (osteogenic sarcoma) is the commonest primary malignant bone tumour (excluding myeloma). It is a high-grade tumour whose malignant cells produce osteoid. It has a bimodal age distribution: chiefly adolescents/young adults (10–20 years) during the growth spurt, and a second peak in the elderly (often secondary to Paget’s disease or previous irradiation). It arises in the metaphysis of long bones, most commonly around the knee (distal femur, proximal tibia) and proximal humerus.

Osteosarcoma of the metaphysis around the knee, showing a ‘sunburst’ spiculated periosteal reaction and Codman’s triangle where the lifted periosteum lays down new bone.

Clinical Features

A young patient with progressive pain (often worse at night) and a firm, tender, warm swelling near a large joint, sometimes with a history of trivial trauma that draws attention to the area. There may be limitation of movement and, occasionally, a pathological fracture. Systemic features are usually late.

Investigations

• Radiographs show a metaphyseal lesion with bone destruction and new-bone formation, a sunburst/spiculated periosteal reaction and Codman’s triangle, with cortical breach and a soft-tissue mass.
• MRI of the whole bone defines intramedullary extent and skip lesions
• CT chest and bone scan/pet stage for metastases (the lung is the commonest site).
• Alkaline phosphatase is often raised.
• Biopsy confirms the diagnosis (malignant osteoid-producing cells).

Management

Modern treatment is neoadjuvant (pre-operative) chemotherapy → surgical wide excision (limb-salvage with endoprosthetic replacement or biological reconstruction wherever a safe margin is achievable, otherwise amputation) → adjuvant (post-operative) chemotherapy. The degree of tumour necrosis in the resected specimen after neoadjuvant chemotherapy is an important prognostic indicator. This multi-agent chemotherapy approach has transformed survival from <20% (surgery alone) to around 60–70% in non-metastatic disease.

Prognosis

Prognosis depends on stage (especially the presence of metastases), tumour grade, resectability and the histological response to chemotherapy. Non-metastatic, chemo-responsive tumours that are widely excised do best; the lungs are the dominant site of relapse.

• Commonest primary malignant bone tumour; adolescents (+ elderly Paget/radiation).
• Metaphysis around the knee; osteoid-producing; sunburst + Codman’s triangle; ↑ ALP.
• Metastasises early to lungs — stage the chest.
• Treat with neoadjuvant chemo → wide excision (limb salvage) → adjuvant chemo.
• Relatively radioresistant; % necrosis after chemo is prognostic; survival ~60–70% if non-metastatic.