Metformin in Conjunction With Stereotactic Radiotherapy for Early-stage Non-small Cell Lung Cancer: Long-term Results of a Prospective Phase II Clinical Trial

Background/Aim: Non-small cell lung cancer (NSCLC) is increasingly detected in early stages and there is interest in improving outcomes with stereotactic body radiotherapy (SBRT). As metformin affects NSCLC signaling pathways, it might alter the metabolism of NSCLC treated with SBRT. This study investigated the long-term outcomes of a phase II clinical trial evaluating metformin in conjunction with SBRT for early-stage NSCLC. Patients and Methods: The trial evaluated patients with American Joint Commission on Cancer (AJCC) 7th edition Stage I-II, cT1-T2N0M0 NSCLC who were randomized 6:1 to receive metformin versus placebo in conjunction with SBRT. The outcomes analyzed included local failure (LF), progression-free survival (PFS), overall survival (OS), and Common Terminology Criteria for Adverse Events (CTCAE) version 4 toxicities. Results: There were 14 patients randomized to the metformin arm and one to the placebo. Median follow-up was four years. In the metformin group, the median PFS was 4.65 years [95% confidence interval (CI)=0.31-5.93] and median survival was 4.97 years (95%CI=3.05-4.61). Five year PFS was 27.8% (95%CI=5.3-57.3%) and OS was 46.0% (95%CI=16.0-71.9%). The one patient randomized to placebo was alive and without progression at five years. There were no LFs in the primary SBRT treatment volumes and no CTCAE version 4 Grade >= 3 adverse events. Conclusion: Outcomes of SBRT and metformin for earlystage NSCLC were similar to historic controls. These findings along with the results of the NRG-LU001 and OCOG randomized trials do not support the therapeutic use of metformin for NSCLC.