The RB gene is located at chromosome 13q14 which spans more than 150kb, with one interal gap, and its product is a phosphoprotein of about 110kD which is constantly expressed in normal retina cells. The RB Protein can specifically bind to SV40 large T, E1A and E7 antigens. The deficiency of the RB gene is the cause of retinoblastoma. Besides, RB gene mutations are detected in osteosarcomas, breast carcinomas, small-cell lung cancer (SCLC) , soft-tissue sarcomas and hematopoietic proliferative disorders. The tumorigenicity can be partially or totally suppressed by introducing the RB gene into the tumor cells.