Abstract
BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) is frequently associated with diabetes mellitus (DM), and their prognosis remains particularly poor. Metformin, a widely used antidiabetic agent, has demonstrated anti-tumor effects through multiple mechanisms and has been associated with improved outcomes in various malignancies. In this study, we investigated retrospectively survival outcomes and intra-tumoral infiltration patterns of various immune cells in diabetic patients who underwent curative resection of PDAC, comparing those who received metformin with those who did not. METHODS: A total of 65 diabetic patients who underwent curative resection for invasive PDAC were retrospectively analyzed. Among them, 17 patients received metformin, while 48 did not. Recurrence-free survival (RFS) and overall survival (OS) were compared between the two groups. Following propensity score matching, tumor-infiltrating CD3(+) and CD8(+) T cells were assessed by immunohistochemistry (IHC), and their densities were compared between metformin users and non-users. RESULTS: Patients in the metformin group showed significantly prolonged RFS [hazard ratio (HR) =0.42, P=0.03] and OS (HR =0.421, P=0.03) compared to those in the non-metformin group. Multivariate analysis identified metformin use as an independent prognostic factor for both RFS (HR =0.40, P=0.02) and OS (HR =0.21, P=0.02). The survival benefit of metformin was particularly evident in patients who underwent upfront surgery, whereas not significant in those who received neoadjuvant therapy. Immunohistochemical analysis revealed a significantly higher density of CD8(+) T cells (650.7 vs. 269.9/mm(2), P<0.001) with an increased CD8/CD3 ratio in resected tumors from metformin-treated patients compared to non-users (58.9% vs. 44.8%, P<0.001). This trend was kept in patients who underwent upfront surgery, while less pronounced in patients treated with neoadjuvant therapy. CONCLUSIONS: Metformin may enhance the infiltration of cytotoxic CD8(+) T cells into the tumor microenvironment and improve the prognosis of diabetic patients with PDAC, particularly in those undergoing upfront surgical resection.