DIABETES-MELLITUS AND COLORECTAL-CANCER RISK

The relationship between diabetes mellitus and the risk of colorectal cancer was investigated in a multicenter case-control study, conducted in Italy between 1992 and 1996 on 1225 cases of incident, histologica lly confirmed colon cancer, 728 cases of rectal cancer, and 4154 contr ols, who were in the hospital for acute, nonneoplastic diseases. Overa ll, 66 (5.4%) cases of colon cancer, 50 (6.9%) cases of rectal cancer, and 185 (4.4%) controls reported a history of diabetes. The correspon ding multivariate odds ratios (ORs) were 1.2 [95% confidence interval (CI), 0.8-1.6] for colon, 1.5 (95% CI, 1.1-2.2) for rectal, and 1.3 (9 5% CI, 1.0-1.6) for all colorectal cancers. No association was observe d for subjects who were diagnosed with diabetes at ages of <40 years ( 7 cases and 27 controls, OR = 0.9). The OR was 1.4 (95% CI, 1.1-1.7) f or subjects who were diagnosed with diabetes at ages of greater than o r equal to 40 years and were likely to have non-insulin-dependent diab etes. The association was also stronger (OR = 1.6; 95% CI, 1.1-2.3) am ong subjects whose diabetes was diagnosed 10 or more years in advance and who were greater than or equal to 60 years old at the time of colo rectal cancer diagnosis. None of the other covariates, including sex, education, body mass index, physical activity, energy intake, alcohol drinking, and fiber intake, showed any appreciable modifying effect. T hus, this uniquely large case-control study of colorectal cancer confi rms that subjects with non-insulin-dependent diabetes mellitus have a slightly increased risk of colorectal cancer. More importantly, allowa nce for a large number of identified potential confounding factors, in cluding body mass index, diet, and physical activity, could not explai n the excess colorectal cancer risk among subjects with diabetes melli tus. These findings have plausible biological correlations because ins ulin-like-growth factor-I is a promoter of colon tumor cell growth in vitro.