Incidence of diabetes among patients with colorectal cancer.

Abstract

393 Background: Emerging data show an increasingly recognized risk of colorectal cancer (CRC) in patients with type 2 diabetes (DM) likely due to common biologic pathways. Few data are available on DM incidence among patients with CRC. Our objective was to determine whether patients with CRC have a higher incidence of DM compared to those without CRC. Methods: We conducted a population-based retrospective cohort study in Ontario, Canada, using administrative databases comparing the incidence of DM among all CRC patients identified in the Ontario Cancer registry from Jan 1, 2002 to Dec 31, 2011 with an age-matched control population without CRC. We used Cox proportional hazard to study the association. We modeled the effect of CRC on the cause-specific hazard of developing DM and censored subjects at the time of a competing event. Subgroup analysis was performed on patients receiving chemotherapy vs. not, metastatic disease vs. not and colon vs. rectal cancer. Results: We identified 39,707 persons with CRC and 198,535 controls. The mean age was 68 and 48.6% were female. We found an overall DM incidence of 8.7% over a mean follow up time of 4.8 years. On multivariable analysis, the effect of CRC on the instantaneous hazard of the DM incidence varied over time, and thus we estimated instantaneous hazard ratios (IHR) for years 1-5 of follow up. The risk of DM among CRC patients was significantly higher than controls for at least five years post CRC diagnosis. The overall DM incidence was higher in patients with no metastasis (10.6% vs 8.6%, p<0.01), and lower in patients who received chemotherapy (8.0% vs 9.0%, p<0.01). Conclusions: This is among the first study to report an increased DM incidence among CRC survivors. This association may be due to common risk factors rather than a treatment effect, as the risk remains elevated for at least five years post diagnosis. The hazard may be underestimated, as patients with advanced cancer may not be formally diagnosed with DM. These results strengthen our understanding of the common biologic pathway of both diseases and have major implications for survivorship care in patients with CRC. [Table: see text]