Study of Vimseltinib for Tenosynovial Giant Cell Tumor

Inclusion Criteria: 1. Patients ≥18 years of age 2. TGCT for which surgical resection is not an option (tumor biopsy to confirm diagnosis required if no histology/pathology available at screening) 3. Symptomatic disease as defined as at least moderate pain or at least moderate stiffness (defined as a score of 4 or more, with 10 describing the worst condition) within the screening period and documented in the medical record 4. Participants should complete 14 consecutive days of questionnaires during the screening period and must meet minimum requirements as outlined in study protocol 5. Must have stable analgesic regimen, as judged by the investigator, for at least 2 weeks prior to first dose of study drug 6. Must have measurable disease, as per RECIST Version 1.1, with at least one lesion having a minimum size of 2cm 7. Adequate organ and bone marrow function 8. If a female of childbearing potential, must have a negative pregnancy test prior to enrollment and agree to follow the contraception requirements 9. Must provide signed consent to participate in the study and is willing to comply with study-specific procedures 10. Willing and able to complete the patient-reported outcome (PRO) assessments on an electronic device Exclusion Criteria: 1. Previous use of systemic therapy (investigational or approved) targeting colony-stimulating factor 1 (CSF1) or colony-stimulating factor 1 receptor (CSF1R); previous therapy with imatinib and nilotinib is allowed 2. Received therapy for TGCT, including investigational therapy during the screening period. Participated in a non-TGCT investigational drug study within 30 days of screening. 3. Known metastatic TGCT or other active cancer that requires concurrent treatment (exceptions will be considered on a case-by-case basis) 4. QT interval corrected by Fridericia's formula (QTcF) \>450 ms in males or \>470 ms in females or history of long QT syndrome 5. Concurrent treatment with any study-prohibited medications 6. Major surgery within 14 days of the first dose of study drug 7. Any clinically significant comorbidities 8. Active liver or biliary disease including nonalcoholic steatohepatitis (NASH) or cirrhosis 9. Malabsorption syndrome or other illness that could affect oral absorption 10. Known active human immunodeficiency virus (HIV), acute or chronic hepatitis B, acute or chronic hepatitis C, or known active mycobacterium tuberculosis infection 11. If female, the participant is pregnant or breastfeeding 12. Known allergy or hypersensitivity to any component of the study drug 13. Contraindication to MRI