Background: Diabetes mellitus is associated with an increased incidence of colorectal cancer, but the impact of diabetes mellitus on colorectal cancer prognosis is not clear.
Objective: We conducted a meta-analysis of observational studies to examine the association between preexisting diabetes mellitus and colorectal cancer all-cause mortality, cancer-specific mortality, and recurrence.
Data sources: Medline and Embase were searched through August 22, 2012.
Study selection: We included studies reporting all-cause mortality, cancer-specific mortality, disease-free survival, or recurrence in patients who have colorectal cancer according to diabetic status.
Intervention: Meta-analyses were performed by the use of random-effects models.
Main outcome measures: The primary outcomes measured were all-cause mortality, cancer-specific mortality, and disease-free survival.
Results: Twenty-six articles met our inclusion criteria. Patients with colorectal cancer who had diabetes mellitus had a 17% increased risk of all-cause mortality (relative risk, 1.17; 95% CI, 1.09-1.25) and a 12% increased risk of cancer-specific mortality (relative risk, 1.12; 95% CI, 1.01-1.24) in comparison with those who did not have diabetes mellitus. Those with diabetes mellitus also had poorer disease-free survival (relative risk, 1.54; 95% CI, 1.08-2.18) compared with their nondiabetic counterparts. In subgroup analyses, diabetes mellitus was associated with all-cause mortality in both rectal (relative risk, 1.24; 95% CI, 1.07-1.29) and colon cancer patients (relative risk, 1.17; 95% CI, 1.07-1.29). Sensitivity analyses including only patients with nonmetastatic disease identified stronger associations between diabetes mellitus and both all-cause (relative risk, 1.32; 95% CI, 1.21-1.44) and cancer-specific (relative risk, 1.27; 95% CI, 1.06-1.52) mortality.
Limitations: Some studies had short follow-up or did not report mean or median follow-up. The included studies were heterogeneous in study population, diabetes mellitus diagnostic criteria, and outcome ascertainment.
Conclusion: Patients with colorectal cancer who have diabetes mellitus are at greater risk for all-cause and cancer-specific mortality and have worse disease-free survival than those who do not have diabetes mellitus. Studies are warranted to determine whether the proper treatment could attenuate the excess mortality among patients with colorectal cancer who have diabetes mellitus.