Oncological benefit of metformin in patients with pancreatic ductal adenocarcinoma and comorbid diabetes mellitus

Purpose Some clinical studies have suggested that metformin improved prognoses in several cancers. This study aimed to identify prognostic factors for pancreatic ductal adenocarcinoma (PDAC) and determine the utility of metformin administration. Methods Between January 2007 and December 2015, 373 consecutive patients underwent curative surgery for PDAC. Among the patients, 121 were diagnosed as having diabetes mellitus (DM) before surgery. The characteristics and overall survival (OS) between patients with and without DM were compared retrospectively. Based on their metformin intake, patients with DM were divided into two groups. OS rates between patients with and without metformin intake were compared. Univariate and multivariate analyses were performed to identify prognostic factors for OS among all patients and those with PDAC and DM. Results No significant differences in the 5-year survival rates between patients with and without DM were observed. Among the 121 patients with DM, 18 received metformin and 103 did not (other medications group). The 5-year survival rate was significantly better in the metformin group than in the other medications group (66.7% and 24.4%, respectively; p = 0.034). Multivariate analysis identified pN1 (p = 0.002), metformin administration (p = 0.022), and microvascular invasion (p = 0.023) as independent prognostic factors for OS in the patients with DM. Matched-pair analysis showed that OS tended to be better in the metformin group than in the other medications group (p = 0.067). Conclusions History of metformin intake may contribute to favorable prognosis in patients with PDAC and pre-existing DM.