Background: The incidence of cancer increases with age in both humans and laboratory animals. A clear understanding of the causes of the age-related increase in cancer incidence is needed to develop a strategy for primary cancer prevention.
Methods: We summarized the data available in the literature and our own experience in hormonal metabolic shifts in organisms and disturbances at tissue and cellular levels observed in natural aging and in different types of carcinogenesis in vivo.
Results: There are incongruent patterns of age-related distribution of tumors in different organs and tissues. Aging may increase or decrease the susceptibility of various tissues to initiation of carcinogenesis and usually facilitates promotion and progression of carcinogenesis. Aging may predispose to cancer by at least two mechanisms: tissue accumulation of cells in late stages of carcinogenesis and alterations in internal homeostasis, in particular, alterations in immune and endocrine system. Increased susceptibility to the effects of tumor promoters is found in both aged animals and aged humans, as predicted by the multistage model of carcinogenesis.
Conclusions: Aging is associated with a number of events at the molecular, cellular and physiologic levels that influence carcinogenesis and subsequent cancer growth. A clearer understanding of these events will help in predicting and treating cancer more effectively.