However, incidence of many cancers levels off after age 80, suggesting the possibility of intrinsic resistance to the development of cancer in late life or some selection bias. The age-related increase in cancer incidence predicts that as the U.S. population ages, cancer incidence will continue to increase. There may be increased susceptibility to carcinogens, possibly caused by decreased DNA repair. Multiple genetic changes are necessary for the development of cancer, most clearly exemplified by the stepwise genetic changes shown by many colon polyps progressing to cancer. The exponential rise in many cancers with age fits with an increased susceptibility to the late stages of carcinogenesis by environmental exposures.
Controversy continues over whether cancer is less aggressive in the elderly.
Yet, death occurs with smaller tumor burdens. The part of cancer prevention we know the most about is the avoidance of toxins that induce or promote cancer. Induction refers to the earliest genetic change induced by a carcinogen. Promotion refers to cell growth induction that fixes and then further alters the genetic abnormality. Both may be necessary to create a cancer.