Abstract IA27: Metformin use and pancreatic cancer survival: Are there racial differences?

Abstract

Abstract Background: The effect of metformin use on survival among pancreatic ductal adenocarcinoma (PDAC) patients is controversial. Further, there are no data on African American patients. To address these, we analyzed data from the United States Veterans Health Administration (VHA). Methods: We performed a population-based retrospective cohort study evaluating survival among 3,811 PDAC patients with pre-existing diabetes mellitus (DM), diagnosed with PDAC within the VHA between 1998 and 2013. We calculated hazard ratios (HRs) and 95% confidence intervals (CIs) using multivariable adjusted conventional Cox proportional hazards regression as well as the time-varying Cox proportional hazards regression to control for immortal time bias and confounders. All statistical tests were two-sided. Results: In multivariable adjusted analyses using the conventional Cox model, there was an artificial survival benefit associated with metformin use: HR= 0.89 (95%CI 0.83-0.98, p-value=0.01). In multivariable adjusted analyses using the time-varying Cox model, metformin use was not associated with survival: HR=1.05 (95%CI 0.92-1.14, p-value=0.28). Results were similar among non-Hispanic white patients: HR=1.05 (95%CI 0.96-1.14, p-value=0.26) and African American patients: HR=1.01 (95%CI 0.86-1.19, p-value=0.88). Among patients who were metformin naïve at the time of PDAC diagnosis (N=1158), metformin use was associated with improved survival in non-Hispanic white: HR=0.78 (95%CI 0.61-0.99, p-value=0.04), but not African American patients: HR=1.20 (95%CI 0.75-1.93, p-value=0.45). The survival benefit among non-Hispanic whites was limited to patients with metastatic disease: HR=0.67 (95%CI 0.44-1.01, p-value=0.055). Among African American patients with metastatic disease, HR was 1.30 (95%CI 0.77-2.53, p-value=0.28). There was an interaction between race and metformin use in patients with metastatic disease (p-interaction=0.05). Conclusions: Although metformin use was not associated with survival in patients with PDAC, the survival benefit limited to non-Hispanic white patients who were metformin naïve at the time of diagnosis deserves further study in a racially diverse study population. Citation Format: Kenneth R. Carson, Adetunji T. Toriola, Suhong Luo, Theodore Thomas, Bettina F. Drake, Su-Hsin Chang, Kristen M. Sanfilippo. Metformin use and pancreatic cancer survival: Are there racial differences? [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr IA27.