Background: Diabetes mellitus increases the risk of incident colorectal cancer, but it is less clear if pre-existing diabetes mellitus influences mortality outcomes, recurrence risk, and/or treatment-related complications in persons with colorectal cancer.
Methods: We performed a systematic review and meta-analysis comparing colorectal cancer mortality outcomes, cancer recurrence, and treatment-related complications in persons with and without diabetes mellitus. We searched MEDLINE and EMBASE through October 1, 2008, including hand-searching references of qualifying articles. We included studies in English that evaluated diabetes mellitus and cancer treatment outcomes, prognosis, and/or mortality. The initial search identified 8,208 titles, of which 15 articles met inclusion criteria. Each article was abstracted by one author using a standardized form and re-reviewed by another author for accuracy. Authors graded quality based on pre-determined criteria.
Results: We found significantly increased short-term perioperative mortality in persons with diabetes mellitus. In the meta-analysis of long-term mortality, persons with diabetes mellitus had a 32% increase in all-cause mortality compared to those without diabetes mellitus (95% CI: 1.24, 1.41). Although data on other outcomes are limited, available studies suggest that pre-existing diabetes mellitus predicts increased risk of some post-operative complications as well as 5-year cancer recurrence. In contrast, there is little evidence that diabetes confers increased risk for long-term cancer-specific mortality.
Conclusions: Patients with colorectal cancer and pre-existing diabetes mellitus have an increased risk of short- and long-term mortality. Future research should determine whether improvements in prevention and treatment of diabetes mellitus will improve outcomes for colorectal cancer patients.