Role of pre-existing type 2 diabetes in colorectal cancer survival among older Americans: a SEER-Medicare population-based study 2002–2011

Purpose: Type 2 diabetes mellitus (diabetes) is a common comorbid condition among older adult colorectal cancer (CRC) patients, yet its effects on CRC mortality have not been adequately examined. This study aims to investigate the association between pre-existing diabetes, with and without complications, and CRC mortality. Methods: Medicare beneficiaries 67 years and older diagnosed with CRC between 2002 and 2011 were studied using the Surveillance, Epidemiology, and End Results (SEER)-Medicare datasets. Pre-existing diabetes was ascertained using validated algorithms. Cox proportional hazards models were used to compare all-cause and CRC-cause-specific death risk differences in relation to prior diabetes diagnosis and diabetes severity (with and without complications) with adjustment for relevant patient demographics and disease characteristics. Results: Analyses included 93,710 CRC patients. Among the study population, 22,155 (24%) had diabetes prior to CRC diagnosis and 4% had diabetes-related complications (neuropathy, nephropathy, retinopathy, or peripheral circulatory disorders). All-cause CRC mortality was significantly higher among diabetic patients compared with non-diabetic patients (hazard ratio (HR) = 1.20; 95% confidence interval (CI) = 1.17–1.23). The results were more pronounced for diabetes with complications (HR = 1.47; 95% CI = 1.34–1.54). Diabetic patients with complications were 16% more likely to die of colorectal cancer compared with patients without diabetes (HR = 1.16; 95% CI = 1.08–1.25). Conclusion: Pre-existing diabetes contributes to poorer all-cause mortality among CRC patients and increased mortality from CRC among those with diabetes and complications. Opportunities exist to incorporate diabetes prevention and management interventions during CRC treatment phases among older adults.