Determination of factors responsible for the declining incidence of colorectal cancer

INTODUCTION: After rising for IS pears in the United States, the incidence of colorectal cancer began to fall in 1986 and has continued to drop since then. This report contains an analysis of the pattern of declining colorect al cancer risk by colorectal subsite, race, and gender and a time trend inv estigation of suspected risk modifiers of colorectal cancer. METHOD: Colore ctal cancer incidence data were obtained from the Surveillance, Epidemiolog y, and End Results Public Use Files from 1973 to 1994. The following exposu re variables were assessed, focussing principally on the period 1970 to 198 0. dietary fat, fiber, ethanolic beverages, vitamin A, vitamin C, iron, cal cium, estrogen, aspirin, energy intake, body mass index, serum cholesterol, body iron stores, cholecystectomy, constipation, cigarette use, physical a ctivity and colonoscopic polypectomy. Data sources used in these analyses w ere principally National Health and Nutrition Examination Surveys I, II, an d III. RESULTS: After 1985 colorectal cancer incidence declined predominant ly in the distal colorectum almost equally in both white males and white fe males. Some exposures remained unchanged or trended in the wrong direction (dietary fat, calcium, ethanol, energy intake, physical activity, overweigh t prevalence, and cholecystectomy). Others did not apply equally to both ge nders (estrogen, aspirin, ethanol, calcium, and cholecystectomy). Others ma y become significant in the future, such as aspirin, estrogen, or calcium, because their supplementation is now prevalent, but were not in 1970 to 197 5. Of all the risk factors or interventions assessed, the one most consiste nt with the observed pattern of change is increased use of colonoscopic pol ypectomy. CONCLUSION: The best method to diminish the incidence of colorect al cancer today may be to increase the use of screening colonoscopy and pol ypectomy.