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.