Cancer and aging.

It is widely accepted that the incidence of cancer increases with aging and many hypotheses have been put forward to explain this association. A review of the literature, however, shows that the relationship between cancer and aging has to be reappraised. Although the incidence of most cancers increases during the second half of the animal life span, only with a few does it increase progressively with senescence in humans as well as in animals. As a matter of fact in many cases the incidence does not vary, levels off or even decreases in old individuals. Late developing tumors also seem in many instances to progress more slowly. Thus it seems that the incidence of cancer is related to age rather than to aging and that some conditions may be created during senescence which oppose the development of some cancers.