Chromosome 13 homozygosity in osteosarcoma without retinoblastoma.

We provide evidence that some human osteosarcomas arise subsequent to the development of homozygosity at loci on the long arm of chromosome 13. The resulting chromosome 13q homozygosity allows the phenotypic expression of any recessive allele on that chromosome. Clinical evidence suggests that it is the retinoblastoma locus within 13q14 that is involved in the formation of these bone tumors.