Introduction
Osteosarcoma is the most common primary malignant bone tumour of non-haematopoietic origin. It is a malignant mesenchymal tumour that produces osteoid, that is, immature bone matrix, directly from the tumour cells. This note covers the classification, the radiological picture, diagnosis and differential diagnosis, staging, treatment and prognosis that a good oral answer should contain.
Definition and epidemiology
Osteosarcoma is a malignant tumour of osteoblastic lineage that forms malignant osteoid and often bone. It has a bimodal age distribution, with the main peak in the second decade of life (adolescents during the growth spurt) and a smaller peak in older adults, usually related to Paget disease or prior radiation. It is slightly more common in males.
- Typical sites: metaphysis of long bones, most often the distal femur, proximal tibia and proximal humerus.
- Less often: flat bones such as the pelvis, and the jaw in older patients.
Classification
Classification is by histological subtype, grade and location. Conventional high-grade intramedullary osteosarcoma is the most common form. The table summarises the main subtypes that an examiner may ask about. Radiologically, three types are described by the dominant appearance: osteolytic, osteoplastic (sclerotic) and mixed (see the radiological picture).