Makindo Medical Notes

Osteosarcoma is a tumour that is radio-resistant, meaning that radiotherapy is typically not used as part of the treatment regimen.

About

• Osteosarcoma is the most common primary malignant bone tumour seen in adolescents and young adults.
• It typically arises in the metaphysis of long bones, particularly near growth plates, where rapid bone growth occurs during puberty.
• The tumour produces immature bone, known as osteoid, as part of its pathological process.

Aetiology

• Osteosarcoma is often associated with genetic predispositions, particularly in individuals with Li-Fraumeni syndrome, which involves germline mutations in the TP53 tumour suppressor gene.
• Other genetic conditions linked to osteosarcoma include hereditary retinoblastoma (RB1 gene mutations) and Paget's disease of bone in older adults.
• Exposure to ionizing radiation is a known risk factor, as previous radiation therapy can increase the risk of osteosarcoma development.
• The tumour is characterized by the production of immature bone (osteoid) by malignant cells, which disrupts normal bone structure and growth.
• It most commonly affects the distal femur, proximal tibia, and proximal humerus.

Clinical Features

• Osteosarcoma most often affects adolescents between the ages of 15-18, with a slight male predominance.
• Localized pain and swelling: These are the most common presenting symptoms. The pain is often persistent and may be misattributed to growing pains or trauma, leading to delayed diagnosis.
• The most commonly affected sites include the distal femur, proximal tibia, and humerus, which are areas of rapid bone growth.
• In more advanced cases, patients may present with visible swelling or a palpable mass, along with restricted joint movement.
• Fractures may occur at the tumour site due to bone weakening.

Investigations

• Plain X-ray: Typically shows a "sunburst" appearance due to the spiculated bone growth as the tumour disrupts normal bone architecture.
• Codman’s Triangle: This classic sign is seen on imaging due to the elevation of the periosteum as the tumour grows beneath it.
• Advanced Imaging: CT and MRI are used to assess the extent of the tumour, including local invasion into soft tissues and potential metastases. MRI is especially useful for surgical planning.
• Laboratory Markers: Raised levels of lactate dehydrogenase (LDH) and alkaline phosphatase can be associated with more aggressive disease and may serve as prognostic markers.
• Biopsy: A large-core or open biopsy is required to confirm the diagnosis, as this allows histological examination of the tumour to identify osteoid production.
• Staging: Bone scans and chest CT scans are essential for staging, as the lungs are the most common site of metastasis. Staging helps determine the extent of the disease and guide treatment.

Treatment and Prognosis

• Surgical Resection: Complete surgical resection of the tumour is the cornerstone of treatment. This may involve limb-salvage surgery or, in more severe cases, limb amputation. Advances in surgical techniques have made limb-salvage surgery increasingly feasible.
• Chemotherapy: Because micrometastases are often present at the time of diagnosis, chemotherapy is essential. It is typically administered both before (neoadjuvant) and after (adjuvant) surgery to reduce tumour size and eliminate microscopic disease.
• Radiotherapy: Osteosarcoma is generally considered radio-resistant, meaning that radiotherapy is not typically used as a treatment option.
• Prognosis: The overall prognosis depends on several factors, including the tumour's location and the presence of metastases. Tumors involving the axial skeleton (e.g., spine, skull) have a worse prognosis compared to those affecting the limbs. With modern treatment, the 5-year survival rate for localized osteosarcoma is approximately 60-70%, but this decreases significantly with metastatic disease.

References

• Further information can be found in oncology and orthopedic textbooks.