The cancer problem - Carcinogenesis and prevention from the viewpoint of the natural history of cancer

Cancer is mostly environmental in origin and therefore is theoretically pre ventable by control of environmental conditions. From the viewpoint of the natural history of cancer, the multi-step nature of neoplasia and the gener ally long latent period are stressed. The molecular biology of cancer tells us that neoplasia is a disease of the genes, with each tumor having its ow n series of gene alterations. Numerous carcinogens, mutagens and others, ha ve been identified, and we are now in a good position to promote cancer pre vention. The aim is to postpone clinical manifestations of latent cancer to an older age, and has two aspects: one is elimination of carcinogens from the environment and the other is active efforts to improve the lifestyle an d develop effective chemopreventive agents. For understanding of prevention , elucidation of molecular mechanisms of interactions between genes and env ironmental or dietary compounds for each cancer is essential.