An Open-Label Study of Intra-articular AMB-05X Injections in Subjects With Tenosynovial Giant Cell Tumor of the Knee

Inclusion Criteria:

1. Subject ≥ 18 years
2. A confirmed diagnosis of tenosynovial giant cell tumor (TGCT) of the knee joint
3. Measurable disease based on RECIST v1.1
4. Stable prescription of analgesic regimen
5. Negative urine drug screen (UDS) at Screening and Baseline
6. Women of childbearing potential must have a negative pregnancy test
7. Agrees to follow contraception guidelines
8. Adequate hematologic, hepatic, and renal function, at Screening
9. Willing and able to complete self-assessment instruments throughout the study

Exclusion Criteria:

1. Prior investigational drug use within 4 weeks or 5 half-lives of Baseline
2. Previous use of therapeutics targeting CSF1 or CSF1R or oral tyrosine kinase inhibitors
3. History of extensive knee surgery
4. Active cancer (either currently or within 1 year before Baseline) that requires therapy (e.g., surgery, chemotherapy, or radiation therapy)
5. Metastatic TGCT
6. Hepatitis C virus (HCV) or hepatitis B virus (HBV) or human immunodeficiency virus (HIV)
7. Known active tuberculosis
8. Significant concomitant arthropathy in the affected joint, serious illness, uncontrolled infection, or a medical or psychiatric history
9. Women who are breastfeeding
10. A screening Fridericia-corrected QT interval (QTcF) ≥ 450 ms (men) or ≥ 470 ms (women)
11. MRI contraindications (e.g., pacemaker, loose metallic implants)
12. History of hypersensitivity to any ingredient of the study drug
13. History of drug or alcohol abuse within 3 months before the first dose of study drug
14. Any other severe acute or chronic medical or psychiatric condition or clinically significant laboratory abnormality that may increase the risk associated with study participation/treatment or interfere with interpretation of study results and, in the Investigator's opinion, make the subject inappropriate for this study
15. Subjects who, in the Investigator's opinion, should not participate in the study for any reason, including if there is a question about their ability to comply with study requirements