In order to assess the relationship between obesity and the incidence of certain types of cancer in men and women from different regions of the world, Renehan et al. performed a systematic review and meta-analysis of 221 datasets of prospective observational studies with incident cases of 20 cancer types. A total of 282,137 incident cases were studied. In men, a 5 kg/m2 increase in body mass index (BMI) was associated with the incidence of esophageal carcinoma and of thyroid, colon, and renal cancers. In women, the same increase in BMI was associated with incident esophageal carcinoma and endometrial, gallbladder, and renal cancers. As for incident breast cancer, the associations between obesity and breast cancer incidence were higher in women from the Asia-Pacific regions as opposed to women from North America, Europe, and Australia. A sex-specific association between BMI and colon cancer was also observed, as obese men were more likely to develop colon cancer than obese women. Given the important cancer risk stemming from obesity, the authors of this meta-analysis suggested that the underlying mechanisms linking excess body weight and cancer need to be further studied and managed. This paper was accompanied by an editorial by Larsson and Wolk (Lancet 2008;37:536-7) who suggested potential mechanisms that might link obesity and cancer incidence. They also considered what measure of obesity would better discriminate cancer risk and raised a number of other important, related questions. In addition, they suggested that healthy lifestyle habits should be promoted to prevent cancer incidence and that national cancer plans need to focus on the importance of maintaining a healthy body weight in order to decrease cancer incidence and increase survival.
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