Among HLA class I genes, homozygosity frequencies ranged from 10% (Ewing sarcoma) to 20% (nephroblastoma) for HLA-A, from none (HGG, ependymoma, nephroblastoma) to 7.5% (osteosarcoma) for HLA-B, and from 3.8% (HGG) to 12.2% (NRSTS) for HLA-C, as compared to 14.8, 6.7 and 9.4% of controls, respectively. This evidence concerns the gene HLA-B and ependymoma.