In a study of 4.5 million patients hospitalized at Veterans Affairs hospitals over a 27-year time period, researchers found an increased risk for nearly 20 different cancers in those men who were obese. The study appears in the January/February issue of Cancer Causes and Control. Claudine Samanic and co-workers, all from the National Cancer Institute's (NCI's) Division of Cancer Epidemiology and Genetics, examined medical histories from computerized discharge notes from Veterans Affairs hospitals across the country. They assessed records for over 3.6 million white men and over 800,000 black men. Among obese veterans, they found an increased risk for cancers of the colon and kidney, which have been reported in numerous other studies, but also an increased risk for a number of less common cancers, such as male breast, lower esophagus, gallbladder, thyroid, extrahepatic bile duct, and connective tissue cancers, as well as malignant melanoma, multiple myeloma, chronic lymphocytic leukemia, and acute myeloid leukemia.

For most tumors, the obesity-related patterns of risk were similar among black and white men. The researchers noted that the mechanisms by which obesity predisposes men to cancer are likely to vary by the type of cancer. They postulated that metabolic alterations associated with obesity and excess abdominal fat may be related to the increased risk for some cancers, possibly through the development of insulin resistance and other mechanisms.

The researchers expressed a number of cautions in interpreting the study results, including the lack of a system to follow the men once they have been discharged from the Veterans Affairs hospitals, which may result in incomplete cancer profiles. Further investigation is needed to clarify the impact of excess body weight, particularly on the risk of relatively uncommon forms of cancer, and to determine the mechanisms involved.