Biology of aging as related to cancer.

The relationship of the biology of aging to cancer in older patients is of importance at several levels. The striking increase of cancer incidence with age may be related to a number of biologic factors. Potential age-related etiologic factors include decreased immune surveillance, longer duration of carcinogenic exposure, increased susceptibility of cells to carcinogens, decreased DNA repair, oncogene activation or amplification, and defects in tumor-suppressor genes. Moreover, at the cellular level, the uncontrolled proliferation characteristic of cancer and the reduced proliferation characteristic of senescence may be "opposite sides of the coin," governed by similar mechanisms of gene regulation. The biologic behavior of neoplasma, once initiated, may vary in different age groups depending on tumor type, immune system status, and alterations in other regulatory factors such as angiogenesis. In the clinical approach to the older cancer patient, attention to age-related biologic changes leading to decreased homeostatic reserve, especially in such areas as the hematopoietic, renal, immune, and cardiovascular systems, is essential to the designing of successful therapies.