Alterations of thep53, Rb andMDM2 genes in osteosarcoms

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Abstract
Molecular defects affecting tumor-suppressor genes are an important step in the genesis of sarcomas. For example, inheritance of a defectiveRb orp53 gene predisposes the carrier to develop osteosarcoma, among other malignancies. In this study, we have assessed the occurrence ofp53, Rb andMDM2 alterations in the same samples of osteosarcomas, along with representative samples of various other sarcomas. Point mutations of thep53 gene were found in 13 of 42 osteosarcomas and 1 of 8 leiomyosarcomas, and gross rearrangement of thep53 gene was demonstrated in 5 of 37 osteosarcomas. The retinoblastoma susceptibility gene (Rb) was either rearranged or deleted in 7 of 37 osteosarcomas, 1 of 7 soft-tissue sarcomas and 1 of 4 Ewing sarcomas. Remarkably, 5 of the osteosarcomas havingRb alterations also hadp53 mutations. Amplification and overexpression of theMDM2 oncogene may lead to increasedMDM2-p53 binding resulting in inactivation ofp53 function. A two- to threefold increase in the copy number ofMDM2 was detected in 7 of 37 samples, 5 of which were osteosarcomas. Amplification of theMDM2 gene occurred independently ofp53 mutation; one sample having threefold amplification ofMDM2 also had ap53 mutation. In summary, 34 alterations of thep53, Rb andMDM2 genes were found in 26 of 42 (62%) osteosarcomas.