TP53 and cancer: The clinical application of adenovirus-mediated gene therapies for cancer patients involves the following goals: 1) to establish a normal cell cycle and subsequent apoptosis by delivering tumor suppressor genes such as p53; 2) to overexpress toxic genes that target cancer cells, such as PSA-driven herpes simplex virus thymidine kinase; 3) to enhance host anti-cancer immunity by overexpressing immune modulators; and 4) to induce cell lysis by virus amplification with or without the expression of therapeutic gene(s).