Although diabetes has been associated with an increased risk of colorectal cancer in most epidemiological studies, findings around the strength of the association and sex-diabetes interaction have been inconlusive. In this study, we examined the role diabetes in relation to colorectal cancer (CRC) in a population-based frequency matched case-control study in Newfoundland and Labrador (NL), which is the most homogeneous population with the highest CRC incidence and diabetes prevalence in Canada.

Newly diagnosed and histologically confirmed CRC cases were identified from NL cancer registry. Randomly selected controls through random digit dialing (RDD) were frequency-matched to cases by sex, 5-year age group and ethnicity. All participants were asked to finish a set of self-administered questionnaires including the family history (FHQ) and personal history questionnaires (PHQ). In rare instances where participants were unable to independently finish the questionnaire, a telephone or face-to-face interview was used.

In total, 673 cases (414 men and 259 women) and 720 controls (426 men and 294 women) were recruited between 1999 and 2004 with adjusted response rates of 59.8% and 45.6%, respectively. Bi-variate as well as multivariate logistic regression analyses were performed to assess the effect of diabetes on colorectal cancer after controlling for potential confounding factors. Sex stratified analysis was used to examine the possible sex-diabetes interaction.

Odds ratios (OR) and the corresponding 95% confidence intervals (CI) were derived from multivariate logistic regression model including co-variates of age, country of birth, race, residence, education, income, marital status body mass index (BMI). The results show a significantly increased risk of CRC among those who had diabetes compared with these who did not have diabetes. Overall, 138 cases (20.5%) and 94 controls (13.1%) reported a history of diabetes. The adjusted OR for diabetes was 1.64 (95% CI: 1.21-2.24) in the two-sex combined model. When sex stratified analyses were used, the adjusted odds ratios were similar between the two genders with corresponding ORs for men and women were 1.64 (95% CI: 1.11-2.43) and 1.61 (95% CI: 0.97-2.69). In conclusion, the current study further corroborates previously reported association between diabetes and CRC and the association is not modified by sex.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA