Diabetes mellitus as a risk factor for recurrence or metastases in colorectal cancer: A systematic review

Background/Objectives: Diabetes has been associated with the risk of colorectal cancer, but its role as a risk factor for recurrence or metastasis is unknown. The aim of this systematic review was to examine the risk of pre-existing diabetes in the progression of colorectal cancer, whether local recurrence or metastasis. Methods A summary synthesis was performed in accordance with the Synthesis Without Meta-analysis guideline. The MeSH terms used were diabetes, colorectal neoplasm and metastasis. The studies should include diabetes as a pre-exposure to the diagnosis of colorectal cancer, investigate local recurrence or metastasis of colorectal cancer and be an original observational primary investigation. Results From 626 identified studies, 9 cohort studies were selected, including a total of 16,855 patients. An association of diabetes with a shorter time to recurrence was found in prospective studies of patients with colon cancer only (n = 8,103; HR = 1.35; 95% CI:1.04–1.77). The relationship was not significant in studies with patients with both colon and rectal cancer (n = 1,923) and patients with rectal cancer only (n = 1,950). Regarding the incidence of recurrence, one European study with patients with rectal cancer (n = 53) found an association of diabetes with a significantly higher local recurrence, although not with metastasis. In a study of non-European patients with colon cancer (n = 1,923), no differences were found in the incidence of recurrences based on diabetes status. Conclusions Diabetes may play a prognostic role in colon cancer. Diabetes may be a risk factor for cancer recurrence in Europe, but not in other parts of the world.