The interest on the p53 gene has grown enormously in the last 4 years. It is now known that p53 is directly involved in important cellular functions including regulation of the cell cycle, and that its alteration may be one of the important steps in the initiation of cancer. In this review I will cover briefly basic and clinical aspects related to the p53 gene and protein and explore ways of using the accumulated knowledge for patient diagnosis and monitoring. The literature suggests that it is now appropriate to start assessing the p53 gene status of breast tumors for prognosis. Therapeutic options are at an infancy stage. A new diagnostic approach based on the immune response of cancer patients against mutant proteins is discussed, by using the p53 mutant protein as a model. Although the cancer patient has not as yet benefited directly from the enormous number of investigations on the p53 gene and protein, there is hope that in the long-term these studies will promote the understanding of cancer initiation and progression at the molecular level with a practical return at a later phase.