Exploring Whether Statins or Metformin Influence the Growth of Vestibular Schwannomas

Objective: This study aims to assess whether statins and or metformin impact the growth of vestibular schwannomas (VS).

Study Design: Retrospective case series.

Setting: Single, tertiary care academic hospital.

Patients: Patients diagnosed with a sporadic VS, with at least two MRI studies at least 6 months apart prior to any intervention.

Intervention: Serial MRI studies. Using Brainlab cranial planning software, a combination of three reviewers measured the greatest linear diameter on axial imaging, in addition to manually segmenting each tumor to calculate volumes in serial MRI studies.

Main Outcome Measure: The VS tumor growth, defined as either ≥2 mm increase in tumor size when measuring the greatest axial diameter, or a 20% increase in tumor volume, between consecutive MRI studies, or between the first and last available MRI study. Growth rates in patients, who had evidence per their electronic medical record (EMR) of having been prescribed either a statin or metformin, were compared with growth rates in patients on neither medication.

Results: A total of 426 patients met inclusion criteria, 53.4% of which were women. For all patients, the median age was 61.5 years (IQR: 53.5–68.2 years), the median linear tumor diameter at diagnosis was 11.3 mm (IQR: 6.5–16.4 mm), and the median tumor volume was 0.31 cm³ (IQR: 0.12–0.79 cm³). Reviewing the EMR, 48 patients (11.3%) were taking metformin; 146 patients (34.3%) were taking a statin; and the remainder 232 patients were considered controls. Comparing tumor measurements between raters, the intraclass correlation coefficient (ICC) for linear measurements was 0.934 (95% CI: 0.865–0.967) while for volumetric measurements, it was 0.902 (95% CI: 0.802–0.952). In assessing metformin, utilizing linear measurements, 17.0% of patients demonstrated growth compared with 19.1% of controls (p = 0.844). Utilizing volumetric measurements, 48.9% of patients demonstrated growth as compared with 61.9% of controls (p = 0.112). With regard to statin use, utilizing linear measurements, 13.1% of patients demonstrated growth, which was significantly fewer than the control group in which 22.2% of controls demonstrated growth. (p = 0.032). When utilizing volumetric analysis, 57.2% of statin users demonstrated volumetric growth compared with 62.1% of controls (p = 0.393).

Conclusion: Utilizing linear measurements, VS patients taking a statin demonstrated significantly less VS growth as compared with controls. However, when assessing tumor volumes, there was no significant growth rate between statin users and controls. In regard to metformin usage, neither linear nor volumetric measurements demonstrate any difference in VS growth between patients and controls.