Metformin’s impact on tumor regression grade in diabetic patients with rectal cancer undergoing neoadjuvant chemoradiotherapy

This retrospective study was designed to investigate the impact of metformin use on the efficacy of neoadjuvant chemoradiotherapy in patients with locally advanced rectal cancer. It is a retrospective, single institution study. Patients with rectal adenocarcinoma treated at Chang Gung Memorial Hospital between January 2005 and December 2019 were retrospectively reviewed. Patients were divided into two groups: metformin users (n = 56) and non-metformin users (n = 33). The primary outcome of this study was tumor regression grade (TRG). Secondary outcomes included recurrence rate, T downstage, and disease-free survival (DFS). Patients in the metformin group demonstrated significantly improved tumor regression grade (p = 0.006). However, no significant difference was observed between the two groups in terms of overall survival (OS) or DFS. Further analysis suggested a potential association between metformin dosage and TRG. Metformin appears to influence the response to neoadjuvant chemoradiotherapy in rectal cancer, specifically impacting TRG. Further research is warranted to validate these findings and explore the optimal metformin dosage and treatment regimens.