Purpose

This is a Phase 3 clinical study, which aims to evaluate the effectiveness of an investigational drug called pexidartinib for the treatment of certain tumors for which surgical removal could cause more harm than good. The main purpose of this study is to gather information about the investigational drug pexidartinib, which may help to treat tumors of pigmented villonodular synovitis (PVNS) or giant cell tumor of the tendon sheath (GCT-TS). The study consists of two parts with a follow-up period. In Part 1, eligible study participants will be assigned to receive either pexidartinib or matching placebo for 24 weeks. A number of assessments will be carried out during the course of the study, including physical examinations, blood tests, imaging studies, electrocardiograms, and questionnaires. MRI scans will be used to evaluate the response of the tumors to the treatment. Some subjects, assigned to placebo in Part 1 transitioned to pexidartinib for Part 2. Then a protocol amendment was written to allow only pexidartinib patients to continue into Part 2. Part 2 is a long-term treatment phase in which all participants receive open-label pexidartinib. There was also a follow-up period added to Part 2.