Osteosarcoma is the second most common primary bone tumour, after myeloma.
Epidemiology
Osteosarcoma is the most common bone tumour in children (50% of cases) and is the fifth-most common tumour of adolescents.
'Secondary' osteosarcoma occurs in older adults, typically after exposure to ionising radiation or Paget's disease of bone.
Pathology
Tumours typically arise at the metaphysis of long bones, typically around the knee joint. They can arise in any bone.
The typical microscopic appearance is highly variable; the uniting feature is the production of osteoid. The malignant cells are often highly anaplastic. Conventional osteosarcoma is divided into:
- Osteogenic Osteosarcoma, where the matrix is mostly osteoid
- Fibroblastic Osteosarcoma, where the matrix is mostly collagen
- Chondroblastic Osteosarcoma, where the matrix is mostly cartilaginous
Other variants include:
- Telangiectatic osteosarcoma: Containing vascular spaces and osteoid
- Small cell osteosarcoma: Comprising small cells that resemble Ewing sarcoma, with osteoid formation
Genetic Conditions
Li-Fraumeni syndrome and familial retinoblastoma patients have a high risk of osteosarcoma.
Diagnosis
Patients present with pain that has often been present for weeks to months. Imaging of the involved bone with MRI, CT of the chest, and whole body bone scan are required for staging.
Treatment
Surgery and chemotherapy form the mainstay of treatment.
Choice of neoadjuvant versus adjuvant chemotherapy is not clear; most centres use neoadjuvant treatment to assist with limb preservation. Methotrexate, doxorubicin and cisplatin were used in the most recent oncology trials. (MAP / MAC / MDC).
Surgical excision is required for cure:
- For extremity lesions, a decision regarding limb sparing surgery versus amputation is a common consideration. In general, limb salvage is preferred unless it would compromise the surgical margins. There is no evidence to support one approach over the other.
- For pelvic lesions, hemipelvectomy is used instead of hindquarter amputation due to equivalent results oncologically and better functional outcomes with the former.
- For spine tumours, complete resection is rare and adjuvant therapy may be needed.
Radiotherapy is only utilised when:
- There is an incomplete resection and further resection is not possible
- Surgery is not possible or refused
The dose is 60 Gy in 30 fractions where possible but lower doses may be necessary, for instance around the spine.
Palliative Treatment
About 10-20% of patients are long term survivors with metastatic disease, particularly if there are only pulmonary oligometastases that can be resected.
The remaining patients should be treated palliatively. Radiotherapy may provide local control.
