Obesity and cancer risk among white and black United States veterans

Background: Obesity has been linked to excess risk for many cancers, but the evidence remains tenuous for some types. Although the prevalence of obesity varies by race, few studies of obesity-related cancer risk have included non-white subjects. Methods: In a large cohort of male US veterans (3,668,486 whites; 832,214 blacks) hospitalized with a diagnosis of obesity between 1969 and 1996, we examined risk for all major cancer sites and subsites. Person-years accrued from the date of first obesity diagnosis until the occurrence of a first cancer, death, or the end of the observation period (September 30, 1996). We calculated age- and calendar-year adjusted relative risks (RR) and 95% confidence intervals (CI) for cancer among white and black veterans, comparing obese men to men hospitalized for other reasons, with obesity status as time-dependent. For selected cancers, we performed additional analyses stratified by specific medical conditions related to both obesity and risk of those cancers. To determine whether obesity-related cancer risks differed significantly between white and black men, we evaluated heterogeneity of risk for each cancer site. Results: Among white veterans, risk was significantly elevated for several cancers, including cancers of the lower esophagus, gastric cardia, small intestine, colon, rectum, gallbladder and ampulla of vater, male breast, prostate, bladder, thyroid, and connective tissue, and for malignant melanoma, multiple myeloma, chronic lymphocytic leukemia (CLL), and acute myeloid leukemia (AML). Excess risks initially observed for cancers of the liver and pancreas persisted among men without a history of diabetes or alcoholism. Among black veterans, risks were significantly elevated for cancers of the colon, extrahepatic bile ducts, prostate, thyroid, and for malignant melanoma, multiple myeloma, CLL and AML. Conclusions: Obese men are at increased risk for several major cancers as well as a number of uncommon malignancies, a pattern generally similar for white and black men. Due to the increasing prevalence of obesity and overweight worldwide, it is important to clarify the impact of excess body weight on cancer and to elucidate the mechanisms involved.