P53 is a transcription factor with a molecular weight of 53kDa that can inhibit cell cycle progression or induce apoptosis in response to stress or DNA damage. Disruption of the p53 signalling pathway through various mechanisms is the most common alteration in human cancer occuring in over half of all tumors. The p53 protein is short lived and expressed at low levels in normal cells but accumulates and/or is activated in cells that have undergone genotoxic damage or oncogene activation. Many tumor derived and transformed cell lines express elevated levels of mutant p53 protein.