P53 gene abnormalities in osteosarcoma. The P53 tumor suppressor gene shows the most frequent genetic alteration in human tumors. Mutation, deletion and rearrangement of P53 gene have been found in several types of neoplasm including osteosarcoma. The present study is to clarify the status of abnormalities of this gene in osteosarcoma in China.Forty-six osteosarcomas were collected from 32 male and 14 female patients aged 20.6 years on average. Eight patients had lung metastasis. Immunohistochemistry, Southern blot and contrast flow cytometry were used for the study.Twenty-seven of 46 (58.7%) osteosarcoma specimens showed strongly positive reaction to the MoAb BP53-12 staining (+2 - +3), which indicated overexpression of P53 protein in osteosarcoma. Contrast study with DNA flow cytometry made on osteosarcoma showed that most of the tumors with strongly positive P53 have higher DNA content than those of negative ones. Alterations of the restriction pattern of the P53 gene were detected in 4 of 20 osteosarcomas in the Hind III group and 3 of 24 in the Eco R I group. Three of them were part or whole deletion of the gene and five of them had extraband which indicated rearrangement of the gene.The results of this study showed that overexpression of P53 oncoprotein is one of the most frequent genetic changes in osteosarcoma and P53 oncoprotein expression analysis could be a prognostic parameter in osteosarcoma. P53 gene abnormalities play an important role in the development of transformation and proliferation of osteosarcoma cells.