Effects of metformin and sulfonylureas on overall and colorectal cancer-specific mortality.

Abstract

2599 Background: Preclinical studies have suggested a role for metformin in the treatment of colorectal cancer (CRC). Associations between metformin versus sulfonylurea exposure and mortality (all-cause and colorectal cancer specific) are assessed in this population-based study of patients with a diagnosis of stage I-IV CRC. Methods: National Cancer Registry Ireland records were linked to prescription claims data and used to identify a cohort of patients with incident TNM stage I-IV CRC diagnosed 2001-2006. From this cohort, 2 patient groups were identified and compared for outcomes - those who received a prescription for metformin +/- a sulfonylurea (MET) or a prescription for sulfonylurea alone (SUL) in the 90 days pre CRC diagnosis. Adjusted hazard ratios (HR) with 95% confidence intervals (CI) were estimated using Cox proportional hazards models adjusted for age, sex, stage, grade, site, comorbidities, year of diagnosis, and insulin, aspirin or statin exposure. Analyses were repeated stratifying by stage and site. Results: 5,617 patients with stage I-IV CRC were identified, of whom 369 received a prescription for metformin or a sulfonylurea in the 90 days pre diagnosis (median follow-up 1.6 years; MET: n=257; SUL: n=112). In adjusted analyses metformin exposure was associated with a 28% lower risk of all-cause mortality relative to sulfonylurea exposure (HR 0.72, 95% CI 0.53-0.98) and a non-significant 24% reduction in CRC-specific mortality (HR 0.76, 95% CI 0.52-1.13). In analyses stratified by site, in colon cancer, metformin exposure was associated with a significant one-third reduction in all-cause mortality (HR 0.66, 95% CI 0.46-0.95) and a non-significant reduction in site-specific mortality (HR 0.64, 95% CI 0.40-1.02). No mortality benefit was observed for rectal cancer. The association between metformin exposure and reduced mortality was strongest for stage I/II disease (all-cause mortality: HR 0.56, 95% CI 0.32-0.98; CRC-specific mortality: HR 0.48, 95% CI 0.21-1.11). Conclusions: Pre-diagnosis metformin exposure in CRC patients was associated with a significant reduction in mortality relative to sulfonylurea exposure. This benefit was greatest in patients with colon cancer and early stage disease.