Association of Metformin With the Growth of Vestibular Schwannomas

Objective: To assess whether medication use, specifically statin, metformin, and aspirin, affects the growth of vestibular schwannomas (VSs). Study Design: Retrospective case series. Setting: Single tertiary care academic hospital. Subjects and Methods: Patients were enrolled if they were diagnosed with sporadic VS and had at least 2 magnetic resonance imaging (MRI) studies at a minimum of 6 months apart prior to any intervention. Electronic medical records were reviewed for demographic and medication data. Tumor volumes on MRI studies were assessed via BrainLab iPlan. The primary endpoint was VS tumor growth, defined as a 20% increase in tumor volume, between consecutive MRI studies or between the first and last available MRI study. Predictors of volumetric growth, specifically statin, aspirin, or metformin use, were analyzed with t tests, chi-square test, univariate logistic regression, and multivariate logistic regression. Results: A total of 387 patients met inclusion criteria, 53.5% of whom were women. For all patients, the mean age was 60.6 years (range, 18.2-89.2 years); the mean axial tumor diameter, 11.9 mm (range, 1.7-32.0 mm); and the mean tumor volume, 0.85 cm³ (range, 0.01-13.1 cm³). In review of the electronic medical record, 46 patients (11.9%) were taking metformin; 145 (37.5%), a statin; and 117 (30.2%), aspirin. Among patients taking metformin, 39.1% (18/46) exhibited volumetric growth, as opposed to 58.2% (198/340) of nonusers (P =.014). Metformin (odds ratio, 0.497; P =.036) is significantly associated with reduced VS growth when controlling for aspirin, statin, and tumor size on multivariate logistic regression. Conclusion: Metformin use is associated with reduced volumetric VS growth.