Inclusion Criteria:  ≥12 years of age and weighing at least 40 kg Progressive meningioma that is amenable to volumetric analysis Has either 1) sporadic meningioma with confirmed NF2 mutation; or, 2) confirmed diagnosis of NF2 disease (revised Manchester criteria); or, 3) at least one NF2-related tumor (with pathogenic germline or proven mosaic NF2 variant) Adequate bone marrow function Has provided written informed consent/assent to participate in the study  Exclusion Criteria:  Progressive disease associated with significant or disabling clinical symptoms likely to require surgery or radiation therapy within the next 3 months. Received prior surgery, radiosurgery, or laser interstitial thermal therapy in the target tumor, or immediately adjacent to the target tumor within 6 months prior to screening. Received an anti- tumor agent for meningioma within 3 months, or 5 half-lives (whichever is longer), prior to screening. History of an active malignancy within the previous 3 years except for localized cancers that are considered cured, and, in the opinion of the investigator, present a low risk of recurrence. Received another investigational drug within 30 days prior to screening Pregnant, lactating, or is planning to attempt to become pregnant or impregnate someone during this study or within 90 days after the last dose of IMP.