Introduction: Anastomotic leakage after anterior resection for rectal cancer is a serious and common complication. Meta-analyses suggest a link between diabetes and leakage, but studies lack detail on diabetes duration and treatment. In this population-based study, we aimed to assess the impact of diabetes, as well as medication and long-term glycaemic control, on the incidence and severity of anastomotic leakage.

Methods: This registry-based study included patients from the Swedish Colorectal Cancer Registry who underwent anterior resection for rectal cancer between 2011–2023. Diabetes status were extracted through cross-linking with the National Diabetes Registry. Prevalent diabetes was investigated as a predictive factor. Mixed-effects logistic and ordinal regression was used, considering clustering effects and confounding from demographics, tumour characteristics, and operative approach.

Results: A total of 8160 patients were included, of whom 1023 (13%) had diabetes. Among the latter, 141 (14%) experienced anastomotic leakage within 30 days of surgery, compared to 696 (11%) in patients without diabetes. Diabetes was demonstrated to be predictive of any leakage, with an adjusted OR of 1.40 (95% c.i.: 1.14–1.73). Similarly, diabetes was associated with a common OR of 1.39 (95% c.i. 1.12–1.74), indicating that the odds of a shift from no leakage to leakage without reoperation or from leakage without reoperation to leakage with reoperation, was 1.39 times greater in diabetics.

Discussion: Prevalent diabetes is an independent risk factor of anastomotic leakage after anterior resection for rectal cancer, with a corresponding dose-response relationship for leakage severity. Further analyses are needed to define subgroups at particular risk.