The annual incidence of osteosarcoma in the USA is 5.6 cases per million children <15 yr of age. The highest risk period for development of osteosarcoma is during the adolescent growth spurt, suggesting an association between rapid bone growth and malignant transformation. Patients with osteosarcoma are taller than their peers of similar age.
Although the cause of osteosarcoma is unknown, certain genetic or acquired conditions predispose patients to development of osteosarcoma.
Patients with hereditary retinoblastoma have a significantly increased risk of developing osteosarcoma. The sites of osteosarcoma in these patients initially were thought to be located only in previously irradiated areas, but more recently they have been shown to arise in sites far from the radiation field. Predisposition to development of osteosarcoma in these patients may be related to loss of heterozygosity of the RB gene.
The pathologic diagnosis of osteosarcoma is made by demonstration of a highly malignant, pleomorphic, spindle cell neoplasm associated with the formation of malignant osteoid and bone.