Estimating the number of U.S. incident cancers attributable to obesity and the impact on temporal trends in incidence rates for obesity-related cancers.

BACKGROUND: Reaching the American Cancer Society challenge goal for the nation to reduce cancer incidence by 25% by 2015 will be influenced in part by the epidemic of obesity. The purpose of this study was to estimate the impact of obesity on the number obesity-attributable incident cancers in the U.S. in 2007 and on trends on cancer incidence rates.
METHODS: Using estimated relative risks (RRs) for obesity vs. normal weight/height from published meta-analyses and/or large cohort studies, and the prevalence of obese adults from the latest national surveys, attributable risk percent (ARP) and numbers of obesity-attributed incident cancers in 2007 were estimated. Using the ARPs, the impact of obesity trends on trends in incidence rates for certain obesity-related cancers was estimated for the calendar years (1976-1980 through 2001-2004) for which cancer rates and obesity prevalence rates were available.
RESULTS: An estimated 33,966 new cancers (4% of all estimated cancers) in males and 50,535 (7% of all estimated cancers) in females diagnosed in 2007, or 6% of all cancers, may be potentially attributable to obesity. Without the impact of rising obesity rates, incidence rates might have declined (instead of remaining stable) from 1988-1994 to 2001-2004 for uterus, breast and certain other cancers.
CONCLUSIONS: Obesity may contribute to about 6% of U.S. incident cancers, apparently has affected recent trends in incidence rates for certain cancers, and is important because of increasing prevalence in the U.S. population.