Metformin Potential Impact on the Growth of Vestibular Schwannomas.

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. 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. 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). 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.