The authors concluded that environmental hazards do not seem to play a major role in the overall increase in cancer incidence rates. Comparisons were made between the two time periods with separate evaluations for men and women, each form of cancer, and five age groups for clues as to why rates are changing. Total cancer incidence increased in all the age groups evaluated by the NCI researchers, and while the common cancers of the breast, prostate, and lung caused the bulk of the increase, incidence rates for several less common cancers are also rising. Increasing incidence rates of kidney, testicular, and brain cancers are less easily explained. Kidney cancers are moderately related to smoking, but diagnostic improvements may be partially responsible for the rise in incidence rates.
Diuretic use is suspected as a possible risk factor.
The increasing incidence of brain cancer, mainly in older ages, is due in part to better imaging technology, but further study is needed, especially because there is also an increase in incidence of brain tumors in people under age 35. The incidence rates of some cancers declined. Colon cancer rates decreased for women and middle-aged men, although rates increased among older men. Stomach cancer rates continued their decline due at least partly to increasing availability and consumption of fresh fruits and vegetables. NCI recommends eating five or more servings of fruits and vegetables each day.