Involvement of the retinoblastoma gene in primary osteosarcomas and other bone and soft-tissue tumors. The retinoblastoma (Rb) gene, thought by some to be associated with tumor formation of retinoblastoma as a recessive human oncogene, was investigated in 57 cases using DNA and RNA from primary osteosarcomas and other bone and soft-tissue tumors. Eight of 23 osteosarcoma cases (35%) showed structural alterations of the Rb gene. Three of the eight demonstrated homozygous deletions, and the remaining five cases showed heterozygous deletions. Seven out of eight cases represented deletion of a 7.5-kb HindIII fragment. Northern blot analysis of five cases of osteosarcoma showed that four demonstrated no detectable Rb gene transcription, and one case had a truncated 3.5-kb fragment with a faint 4.7-kb band. In the other 34 cases of bone and soft-tissue tumors, two cases of three malignant fibrous histiocytomas showed an Rb gene abnormality by Southern blot analysis. These results strongly suggest that Rb gene alteration is pertinent to the tumorigenesis of most osteosarcoma cases and some other bone and soft-tissue tumors.