p53 plays a very important role in cell cycle control. When cell is injured by radiation or chemotherapeutic drugs, p53 gene can arrest cell cycle at G1/S phase, which allows more time for DNA repair. If optimal repair is impossible, p53 may trigger programmed cell death to eliminate the damaged cells. Inactivation of the p53 gene by missense mutation or deletion may cause malignant transformation. About 50% of all human neoplasms con- P53 plays a very important role in cell cycle control. When cell is injured by radiation or chemotherapeutic drugs, p53 gene can arrest cell cycle at G1/S phase, which allows more time for DNA repair. If optimal repair is impossible, p53 may trigger Programming cell death to eliminate the damaged cells. Inactivation of the p53 gene by missense mutation or deletion may cause malignant transformation. About 50% of all human neoplasms con-