Abstract
A direct relation between body mass index (BMI) and risk of colorectal adenomas and cancer has been reported, but few studies have had adequate sample size for conducting stratified analyses by sex, family history, colorectal subsite, or features of metachronous lesions. Data from 8,213 participants in 7 prospective studies of metachronous colorectal adenomas were pooled to assess whether the association between BMI and metachronous neoplasia varied by these factors. A statistically significant direct association between BMI and the odds of nonadvanced adenomas (P(trend) < 0.001) was observed, while the relation for advanced adenomas was of marginal significance (P(trend) < 0.07). In sex-stratified analyses, obesity was statistically significantly associated with the odds of any metachronous lesion among men (odds ratio = 1.36, 95% confidence interval: 1.17, 1.58) but not among women (odds ratio = 1.10, 95% confidence interval: 0.89, 1.37). The associations with BMI appeared to be limited to proximal neoplasia, with statistically significant results for BMI and proximal (P(trend) < 0.001), but not distal (P(trend) < 0.85), neoplasia. Exploratory analyses indicated that BMI was significantly related to most histologic characteristics of metachronous adenomas among men but not among women. Our results provide further support for the association between BMI and metachronous colorectal adenomas, particularly among men, thereby indicating that body size may affect colorectal carcinogenesis at comparatively early stages.