A study on retinoblastoma followed by osteosarcoma at multiple sites reported a heterozygous mutation of RB1 gene in all samples, including the retinoblastoma tissues from eye bulbs, chondroblastic osteosarcoma tissue from orbit, osteoblastic osteosarcoma tissue from the tibia, femur, and lung, with no second-hit RB1 mutation found in all samples7. This evidence concerns the gene RB1 and retinoblastoma.