Metformin Does not Affect Outcomes in Patients With Locally Advanced Rectal Cancer Treated With Neoadjuvant Therapy and Resection

Introduction There is emerging evidence that metformin may have a protective effect in patients with cancer. However, its current evidence in locally advanced rectal cancer (LARC) is inconclusive. We aim to assess the effect of metformin on long-term outcomes in patients with LARC who received neoadjuvant therapy and surgical resection.Methods A retrospective review of 324 patients with nonmetastatic LARC who received neoadjuvant therapy and major surgical resection from 2004 to 2018. There were 27 patients who received metformin before surgery and 297 patients who did not receive metformin.Results Metformin users were associated with a significantly higher age, BMI, ASA score, and 30-day readmissions (P < .05). There was no difference in overall survival (OS, P = .18) or disease-free survival (DFS, P = .33) between the two groups. On Cox regression, metformin intake did not predict OS (HR 0.85, 95% CI 0.4-1.77) when controlled for age (HR 1.04, 1.02-1.06), sex (HR 1.13, 0.69-1.85), BMI (HR 0.97, 0.92-1.02), ASA score (HR: 1.7, 1.06-2.73), TNT (HR 0.31, 0.1-0.92), pathological Stage III disease (HR 2.55, 1.51-4.32), extramural vascular invasion (EMVI) (HR 3.06, 1.7-5.5), and adjuvant therapy (HR 0.1, 0.04-0.27 for <25 months OS and HR 0.3, 0.15-0.59 for >= 25 months). Disease-free survival showed a similar trend with no significant effect of metformin (HR 0.77, 0.39-1.52) when controlled for age, sex, BMI, ASA, TNT, Stage III disease, EMVI, and adjuvant therapy.Conclusion Metformin does not affect long-term survival in LARC treated with neoadjuvant therapy followed by surgical resection. Studies with larger sample sizes are needed to validate the findings further.