Increased 30-Day Mortality Risk in Patients With Diabetes Mellitus After Colon Cancer Surgery: A Mediation Analysis

Background: Patients with (versus without) diabetes mellitus who develop colon cancer are at increased risk of dying within 30 days after surgery. Objective: The purpose of this study was to identify potential mediators of the effect of diabetes mellitus on all-cause 30-day mortality risk after surgery for colon cancer. Design: A retrospective cohort study was conducted using the 2013-2015 National Surgical Quality Improvement Program data. Setting: The study was conducted at various hospitals across the United States (from 435 to 603 hospitals). Patients: Patients who underwent resection for colon cancer with or without obstruction based on the National Surgical Quality Improvement Program colectomy module were included. Patients who had ASA physical status classification V or metastatic disease and those who presented emergently were excluded. Patients were classified as "no diabetes,""diabetes not requiring insulin,"or "diabetes requiring insulin."Potential reasons for increased risk of dying within 30 days were treatment related, comorbidity, health behaviors, surgical complications, and biomarkers of underlying disease. Main Outcome Measures: We measured all-cause 30-day mortality. Results: Of 26,060 patients, 18.8% (n = 4905) had diabetes mellitus that was treated with insulin (n = 1595) or other antidiabetic agents (n = 3340). Patients with diabetes mellitus had a 1.57 (95% CI, 1.23-1.99) higher unadjusted odds of dying within 30 days versus patients without diabetes mellitus. In the multivariable model, 76.7% of the association between diabetes mellitus and 30-day mortality was explained; patients with diabetes mellitus were equally likely to die within 30 days versus those without diabetes mellitus (OR = 1.05 (95% CI, 0.81-1.35)). Anemia and sepsis explained 33.7% and 15.2% of the effect of diabetes mellitus on 30-day mortality (each p < 0.0001). Treatment-related variables, cardiovascular disease, surgical complications, and biomarkers played limited roles as mediators. Limitations: The study was limited to larger hospitals, and limited information about duration and type of diabetes mellitus was available. Conclusions: Better management and prevention of anemia and sepsis among patients with diabetes mellitus may reduce their increased risk of death after colon cancer resection.