Objective: To study the association between type 2 diabetes mellitus (T2DM) and colorectal cancer (CRC).
Study design: An international ecological study and a population-based risk analysis.
Methods: Prevalence data for T2DM and incidence data for CRC were collected from 170 countries, and Spearman's correlation was calculated between T2DM and CRC. In the Nan-Hu district of Jia-Xing city, Zhejiang province, China, the incidence of CRC among T2DM patients between 1 January 2002 and 30 June 2002 was identified through record linkage between the Diabetic Surveillance and Registry Database with the Cancer Surveillance and Registry Database. Standardized incidence ratios (SIRs) and 95% confidence intervals were used to estimate the risk of CRC among T2DM patients.
Results: Significant positive correlations (r(s)=0.534 and 0.597 in males and females, respectively) were found between the prevalence of T2DM and the incidence of CRC. Sixty-four cases of CRC were found among 7938 T2DM patients. The SIR for CRC among T2DM patients was 1.588 (95% CI 1.199-1.977). For male T2DM patients, the SIR for CRC was 1.821 (95% CI 1.234-2.408), compared with 1.364 (95% CI 0.85-1.879) among female T2DM patients. Significant increased risks for colon cancer were found, with an SIR of 1.899 (95% CI 1.139-2.658) in male T2DM patients. Female T2DM patients showed a borderline significant risk for colon cancer, with an SIR of 1.687 (95% CI 0.948-2.426). However, no significant associations were found between T2DM and risk for rectal cancer among males (SIR 1.723, 95% CI 0.786-2.66) or females (SIR 0.906, 95% CI 0.235-1.578) (all P>0.05).
Conclusions: T2DM was associated with increased risk for CRC, and this association was more evident for colon cancer and among male diabetic patients.