Preexisting Type 2 Diabetes and Survival among Patients with Colorectal Cancer

Background: Type 2 diabetes increases risk of developing colorectal cancer, but the association of preexisting diabetes with colorectal cancer survival remains unclear. Methods: We analyzed survival by diabetes status at cancer diagnosis among 4,038 patients with colorectal cancer from two prospective U.S. cohorts. Cox proportional hazards regression was used to calculate HRs and 95% confidence intervals (CI) for overall and cause-specific mortality, with adjustment for tumor characteristics and lifestyle factors. Results: In the first 5 years after colorectal cancer diagnosis, diabetes was associated with a modest increase in overall mortality in women (HR, 1.22; 95% CI, 1.00-1.49), but not in men (HR, 0.83; 95% CI, 0.62-1.12; P heterogeneity by sex = 0.04). Beyond 5 years, diabetes was associated with substantially increased overall mortality with no evidence of sex heterogeneity; in women and men combined, the HRs were 1.45 (95% CI, 1.09-1.93) during >5-10 years and 2.58 (95% CI, 1.91-3.50) during > 10 years. Compared with those without diabetes, patients with colorectal cancer and diabetes had increased mortality from other malignancies (HR, 1.78; 95% CI, 1.18-2.67) and cardiovascular disease (HR, 1.93; 95% CI, 1.29-2.91). Only women with diabetes for more than 10 years had increased mortality from colorectal cancer (HR, 1.33; 95% CI, 1.01-1.76). Conclusions: Among patients with colorectal cancer, preexisting diabetes was associated with increased risk of long-term mortality, particularly from other malignancies and cardiovascular disease. Impact: Our findings highlight the importance of cardioprotection and cancer prevention to colorectal cancer survivors with diabetes.

Automated summary

Among patients with colorectal cancer, preexisting diabetes was associated with increased risk of long-term mortality, particularly from other malignancies and cardiovascular disease. The impact of diabetes on survival varied by sex, with women showing a modest increase in overall mortality in the first 5 years after cancer diagnosis. Beyond 5 years, both men and women with diabetes at diagnosis had substantially increased overall mortality.