Long-term all-cause mortality in cancer patients with preexisting diabetes mellitus: a systematic review and meta-analysis.

Context Diabetes mellitus appears to be a risk factor for some cancers, but the effect of preexisting diabetes on all- cause mortality in newly diagnosed cancer patients is less clear. Objective To perform a systematic review and meta- analysis comparing overall survival in cancer patients with and without preexisting diabetes. Data Sources We searched MEDLINE and EMBASE through May 15, 2008, including references of qualifying articles. Study Selection English- language, original investigations in humans with at least 3 months of follow- up were included. Titles, abstracts, and articles were reviewed by at least 2 independent readers. Of 7858 titles identified in our original search, 48 articles met our criteria. Data Extraction One reviewer performed a full abstraction and other reviewers verified accuracy. We contacted authors and obtained additional information for 3 articles with insufficient reported data. Results Studies reporting cumulative survival rates were summarized qualitatively. Studies reporting Cox proportional hazard ratios ( HRs) or Poisson relative risks were combined in a meta- analysis. A random- effects model meta- analysis of 23 articles showed that diabetes was associated with an increased mortality HR of 1.41 ( 95% confidence interval [ CI], 1.28- 1.55) compared with normoglycemic individuals across all cancer types. Subgroup analyses by type of cancer showed increased risk for cancers of the endometrium ( HR, 1.76; 95% CI, 1.34- 2.31), breast ( HR, 1.61; 95% CI, 1.46- 1.78), and colorectum ( HR, 1.32; 95% CI, 1.24- 1.41). Conclusions Patients diagnosed with cancer who have preexisting diabetes are at increased risk for long- term, all- cause mortality compared with those without diabetes.