Aims and Hypothesis — Diabetes is associated with an increased incidence of colorectal cancer (CRC). There exists conflicting evidence regarding the impact of diabetes on CRC-specific mortality (herein also referred to as cancer-specific mortality). The objectives of this study were to determine whether diabetes is associated with a more advanced CRC stage at diagnosis and with higher all-cause and cancer-specific mortality.
Methods — This retrospective cohort study used linked, population-based health databases from Ontario, Canada. Among individuals diagnosed with CRC from 2007 to 2015, we compared the likelihood of presenting with later- (III or IV) vs early- (I or II) stage CRC between patients with and without diabetes adjusting for relevant covariates. We then determined the association between diabetes and all-cause and CRC-specific mortality, after adjusting for CRC stage at diagnosis and other covariates.
Results — Of the 44,178 individuals with CRC, 11,822 (26.7%) had diabetes. After adjustment for CRC screening and other covariates, individuals with diabetes were not more likely to present with later-stage CRC (adjusted OR 0.97, 95% CI 0.93, 1.01). Over a median follow-up of 2.63 (interquartile range [IQR] 0.97–5.10) years, diabetes was associated with higher all-cause mortality (adjusted HR 1.08, 95% CI 1.04, 1.12) but similar cancer-specific survival (adjusted HR 1.0, 95% CI 0.95, 1.06).
Conclusions and Interpretation — Individuals with diabetes who develop CRC are not more likely to present with a later stage of CRC and have similar cancer-specific mortality compared with those without diabetes. Diabetes was associated with higher all-cause mortality in CRC patients, indicating that greater attention to non-cancer care is needed for CRC survivors with diabetes.