Metformin Increases Overall Survival in Patients with Diabetes Undergoing Surgery for Colorectal Cancer

Emerging evidence suggests that metformin decreases the risk of developing colorectal cancer in patients with diabetes, but only few studies have examined potential survival benefits after surgery for colorectal cancer (CRC). The purpose of the study was to examine the association between diabetes and overall survival after resection for CRC. Furthermore, the association between antidiabetic medication and overall survival was examined. Patients diagnosed with CRC between January 1, 2003 and December 31, 2012 were identified through the Danish Colorectal Cancer Group's National Clinical Database (DCCG). The Danish National Patient Register (NPR) records all hospital contacts in Denmark, and the diagnosis of diabetes was identified by combining NPR data with use of antidiabetic drugs identified through the Danish National Prescription Registry and DCCG. The Kaplan-Meier estimator and the Cox regression model adjusted for important clinical risk factors were used. A total of 30,493 patients were included in the study, of which 3391 were diagnosed with diabetes and 1962 were treated with metformin. The adjusted HR of all-cause mortality for the diabetes group was 1.12 (1.06-1.18, p < 0.0001) compared with the nondiabetes group. The adjusted HR was 0.85 (0.73-0.93, p = 0.03) for the metformin-treated group compared with the insulin-treated group. A 12 % increase in all-cause mortality among patients with CRC and diabetes was found. Treatment with metformin was associated with a 15 % decreased all-cause mortality compared with patients with insulin-treated diabetes.