The decline of the clinical incidence of cancers during human senescence.

Neoplastic growth occurs from the very beginning to the end of the human life span, with a predominant age span for the clinical incidence of each cancer. Most cancers are diagnosed during the second half of human life span, but their natural histories start much earlier than their clinical manifestations. The clinical incidence declines after ages 75-80 years. The histology, the evolution, and the distribution of the frequency of the different cancers during the human life span suggest that neoplastic growth is a dynamic process where new variables are continuously created, the result of the interaction of individual genetics, environmental aggressions, and the developmental stages of the human life span. Data suggest that in many instances tumor growth can be looked upon as a deviation from normal development. Mechanisms are described that can explain the decline of the incidence and the progression during senescence in terms of the changes occurring in the human organism during the last developmental stages.