WT1 and osteosarcoma: Another study by Hirabayashi et al., who investigated WT1 peptide vaccination in a mixed group of pediatric solid tumors, including brain tumors (n = 14), rhabdomyosarcomas (n = 5), neuroblastomas (n = 3), osteosarcoma (n = 1) and clear cell sarcoma of the kidney (n = 1), found WT1 and MHC class I expression in 100% and 85% of the tumor specimens, respectively [73].