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Osteosarcoma

Overview
  • Osteosarcomas are malignant mesenchymal tumor characterized by their capacity to form bone or osteoid (unmineralized bone). They represent the second most common bone tumor following multiple myeloma and thus the most common non-hematopoietic bone tumor.
Epidemiology and Classification
  • Osteosarcomas tend to occur in two patient populations: The majority occur without prior warning in adolescents in their second decade whereas a smaller subset occur in the elderly with a prior history of radiation therapy or benign bone disease such as Paget Disease. In either case there is a slight male predominance.
  • Osteosarcomas are also categorized into "classic" and "variant" subsets based on a number of histological and clinical features. The classic subtype refers to those tumors that occur in adolescents around the knees. The variant subset refers to tumors that arise in atypical locations, within the elderly population described above, or those that display non-traditional histomorphologies.
Morphology
  • Classical osteosarcomas arise in the long bones, especially the metaphyses surrounding the knees. Therefore, the distal femur and proximal tibia/fibula are most commonly involved.
  • The characteristic feature of osteosarcoma is the presence of synthesis of disorganized osteiod or mineralized bone by the tumor cells. The malignant cells may assume a large variety of morphologies but are typically spindle-shaped.
  • Osteosarcomas tend to ossify in a radial pattern that is visible on radiography as a "sunburst" pattern. They can also grow rapidly through cortical bone and elevate the periosteum with such speed that only the edges of the tented periosteum have time to reactively ossify, visible as "Codman's Triangle" on radiography.
Clinical Consequences
  • Osteosarcomas typically present as progressive focal pain and soft-tissue swelling that may be triggered by an otherwise minor trauma. In some cases patients may present with pathologic fractures.
  • Osteosarcomas are aggressive tumors and have typically metastasized by the time of diagnosis, typically to other bone foci as well as the lungs. These were almost universally fatal tumors but prognosis has significantly improved with current aggressive chemotherapy regimens.