ABSTRACT
This analysis examined type 2 diabetes (T2D) as a predictor of colorectal cancer (CRC) survival within the Multiethnic Cohort Study. Registry linkages in Hawaii and California identified 5,284 incident CRC cases. After exclusion of cases with pre-existing cancer diagnosis within 1 year and systemic disease, the analytic dataset had 3,913 cases with 1,800 all-cause and 678 CRC-specific deaths after a mean follow-up of 9.3 ± 5.2 years. Among CRC cases, 707 were diagnosed with T2D 8.9 ± 5.3 years before CRC. Cox regression with age as time metric was applied to estimate hazard ratios (HR) and 95% confidence intervals (CI) for T2D status as predictor of CRC-specific and all-cause survival while adjusting for known confounders. Overall, CRC-specific survival was not associated with pre-existing T2D (HR = 0.84; 95% CI = 0.67-1.07). However, a significant interaction was seen for comorbidity (pinteraction = 0.03) with better survival among those without pre-existing conditions (HR = 0.49; 95% CI = 0.25-0.96) while no association was seen in patients with comorbid conditions. All-cause mortality was also not related to pre-existing T2D (HR = 1.11; 95% CI = 0.98-1.27), but significantly elevated for individuals with T2D reporting comorbid conditions (HR = 1.36; 95% CI = 1.19-1.56). Stratification by T2D duration suggested higher CRC-specific and all-cause mortality among participants with a T2D history of ≥10 than <10 years. The findings were consistent across sex and ethnic subgroups. In contrast to previous reports, pre-existing T2D had no influence on disease-specific and all-cause survival among CRC patients. Only participants with additional comorbidity and possibly those with long T2D duration experienced higher mortality related to T2D.