Metformin Potential Impact on the Growth of Vestibular Schwannomas

Objective: Previous work has suggested that metformin may possess antineoplastic properties. This study aims to assess the effect of metformin on the growth of sporadic vestibular schwannomas. Methods: A retrospective cohort study was performed on patients presenting with radiologically confirmed vestibular schwannomas to Stanford medical center between January 1990 and October 2018. Patients who received metformin during the follow-up period were included and were compared with the control group who were not receiving metformin. Tumor progression and hearing loss are primary and secondary outcomes, respectively. Results: A total of 149 patients were analyzed, with 42 patients receiving metformin. The mean age at presentation is 69.6 (+/- 11.7) years. There are 69 (46.3%) females and 80 (53.7%) males and there is no significant age difference between the groups. Tumor size at presentation is similar between both groups, 8 mm (4-13) in control group and 7.5 mm (4-14) in metformin group. The average follow-up period is 34.2 months (18.3-57.8) and 30.3 months (13.6-69.8) in the metformin and control cohorts, respectively, and they are not significantly different. No significant differences between both groups were found in final American Academy of Otolaryngology - Head and Neck Surgery hearing outcome or poor audiogram outcome. Metformin users are significantly less likely to present with tumor growth at final follow-up compared with nonmetformin users (28.6 versus 49.5%, respectively; p = 0.02). Conclusions: This preliminary result suggests metformin may reduce vestibular schwannoma tumor growth rate and shows potential promise as a novel chemotherapeutic agent. Further studies are needed to validate this finding.