(P 43) SAFETY AND EFFICACY WITH VIMSELTINIB IN PATIENTS WITH TENOSYNOVIAL GIANT CELL TUMOR WHO RECEIVED NO PRIOR ANTI-COLONY-STIMULATING FACTOR 1 THERAPY: ONGOING PHASE 2 STUDY

Objective: Vimseltinib is an investigational, oral, switch-control tyrosine kinase inhibitor specifically designed to selectively and potently inhibit the anti–colony-stimulating factor 1 receptor (CSF1R). In the MOTION phase 3 trial, vimseltinib demonstrated statistically significant and clinically meaningful improvements in the primary and all key secondary endpoints vs placebo. Here, we will report long-term safety and efficacy from cohort A of the phase 2 part (expansion; enrollment complete) of an ongoing phase 1/2 study (NCT03069469) for patients with tenosynovial giant cell tumor (TGCT) treated with vimseltinib.

Methods: Patients with symptomatic TGCT not amenable to surgery and no prior anti-CSF1/CSF1R therapy (previous imatinib or nilotinib allowed) received vimseltinib 30 mg twice weekly (recommended phase 2 dose). The primary objectives were safety, tolerability, and antitumor activity (by independent radiological review [IRR] using Response Evaluation Criteria in Solid Tumors version 1.1); antitumor activity by IRR using tumor volume score was a secondary objective.

Results: In cohort A, 46 patients with TGCT with no prior anti-CSF1/CSF1R therapy were enrolled. At a prior data cutoff (June 2023), most treatment-emergent adverse events (TEAEs) were grade 1/2. Grade 3/4 TEAEs (>5% of patients) were increased creatine phosphokinase and hypertension. There was no evidence of cholestatic hepatotoxicity or drug-induced liver injury. Median treatment duration was 21.0 months (range, 0.2–30.3). Antitumor activity was robust (Table). Updated results will be presented, including long-term safety, duration of response, and best overall response with 8 months of additional follow-up.

Conclusion: Vimseltinib is well tolerated and demonstrates robust antitumor activity in patients with TGCT. Updated results are expected to support long-term safety and efficacy of vimseltinib in patients with TGCT not amenable to surgery with no prior anti-CSF1/CSF1R therapy. Previously presented in part at CTOS 2023 and intended update submitted for consideration to ESMO 2024.