Osteosarcoma (Osteogenic sarcoma)

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What is Osteosarcoma?

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Osteosarcoma is a type of bone cancer.

The bones of the body are a specialised form of connective tissue that form the majority of the human skeleton. They are comprised of calcium, phosphate and magnesium within a framework of type I collagen. The size of the skeleton does not tend to increase beyond puberty (when fusion of the skeletal growth plates occur) but bone is a highly metabolically active tissue undergoing constant resorption, formation and remodelling.

The Three major functions of bone can be seen as:

Mechanical- support of tissues, attachment of muscles and enabling movement of the body;

Metabolic- the bone forms the major storage reservoir for calcium and phosphate in the body; and

Protective- bones provide the protective casing for vital internal organs and also for the bone marrow.

Who gets Osteosarcoma?

It is is rare, accounting for less than 0.2% of new malignancies each year. However, it is the most common primary malignant bone tumour. The vast majority of bony malignancies are metastatic. More than 75% occur in patients younger than 20 years (with peaks at 10-14 for girls and 15-18 for boys) but a second smaller peak also occurs in the elderly with sex incidence being a twice as common in males.

Geographically, the tumour is found worldwide.

Predisposing Factors

Genetic factors play a fundamental role in the development of osteosarcoma. Heritable mutations in the p53 germline are associated with the autosomal recessive Li Fraumeni syndrome of familial cancers and patients with mutations in the Rb gene (associated with the development of retinoblastoma) are also at a high risk of developing osteosarcoma. Osteosarcoma also arises with increased frequency in patients with osteogenesis imperfecta.

Other predisposing factors include: Areas of rapid bone growth (as suggested by the location of tumours at sites of maximal bone growth and in regions of Paget's disease); and radiation (especially post-radiotherapy for a solid organ tumour in childhood).

Progression

This type of tumour spreads by vascular invasion and haematogenous dissemination. Lung and distant bone metastases are the most common sites for spread.

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