[Chemoprevention of cancer. Epidemiology and basic research point to new directions].

Cancer transformation of normal cells has been shown to be a multistep procedure, where a primary change is initiated by endogenous or exogenous alteration in nuclear DNA. Further activation of oncogenes or deletion of tumor suppressor genes is then required to transform the normal cell to a proliferating cancer cell. This process requires many years in humans. Epidemiological evidence and case-control studies have pointed to substances with a potential as cancer chemopreventative. Basic science has elucidated possible mechanisms on initiation and promotion of carcinogenesis behind the chemopreventive action of retinoids, other vitamins and selenium. These substances are presently being investigated in intervention studies to prevent cancer in high risk groups and the general population.