OBJECTIVES: Tenosynovial giant cell tumour (TGCT) is a rare, locally aggressive neoplasm caused by upregulation of the colony-stimulating factor 1 (CSF1) gene. Vimseltinib is an oral switch-control tyrosine kinase inhibitor specifically designed to selectively and potently inhibit CSF1 receptor (CSF1R) and was well tolerated by patients in a phase 1/2 study. Here, we evaluate patient-reported outcome measures for patients with TGCT treated with the recommended phase 2 dose (RP2D) of vimseltinib (30 mg twice weekly; NCT03069469).

METHODS: Patients with TGCT not amenable to surgery were treated in 2 cohorts: A (no prior anti-CSF1/CSF1R therapy except imatinib and/or nilotinib) and B (prior anti-CSF1/CSF1R therapy). Pain was evaluated using the brief pain inventory; swelling and stiffness at the site of the tumour were assessed with symptom-specific questions on the numeric rating scale (scale from 0–10 with 0 being none and 10 being worst imaginable). Results at Week 25 are reported.

RESULTS: As of Feb 18, 2022, 57 patients were enrolled: 46 in A (enrollment complete) and 11 in B (enrollment ongoing). In cohort A, 22/46 (48%) and 24/46 (52%) patients had ≥30% improvement in worst and average pain, respectively. In cohort B, 6/9 (67%) patients had ≥30% improvement in both worst and average pain. At baseline, the average score was 5.1 for both swelling and stiffness in cohort A; swelling decreased by 2.5 points and stiffness decreased by 2.0 points. In cohort B, the average baseline scores for swelling and stiffness were 4.0 and 5.0, respectively; swelling decreased by 2.4 points and stiffness decreased by 2.7 points.

CONCLUSIONS: At the RP2D of vimseltinib, patients in both cohorts reported improvement in worst and average pain and joint swelling and stiffness at Week 25. Results support continued evaluation of vimseltinib at this dose level in the ongoing phase 3 MOTION trial (NCT05059262).