Cancer continues to increase throughout the industrial world. Aging of the population, smoking habits, and improvements in diagnosis do not account completely for these patterns. About 5 percent of cancers occur in persons under age 45, while 65 percent of all cancers occur in persons over age 65. For this older age group, many of their most common tumors, in addition to those linked with smoking, are not curable and appear to be increasing in incidence as well as mortality in a number of industrial countries. Evaluating cancer causes by looking at an age-adjusted rate obscures important differences that are occurring at different age groups. In order to reduce the cancer burden further, it is important to look for bona fide explanations of recent shifts in cancer patterns, especially those not related to cigarette smoking or other habits.