TYPE II RAF INHIBITOR TOVORAFENIB IN RELAPSED/ REFRACTORY (R/R) PEDIATRIC LOW-GRADE GLIOMA (PLGG): RESULTS FROM PATIENTS ON A DRUG HOLIDAY (DH) IN THE PHASE 2 FIREFLY-1 TRIAL

Abstract

BACKGROUND: Tovorafenib, a selective, CNS-penetrant, type II RAF inhibitor, received US FDA accelerated approval for r/r BRAF-altered pLGG. Results from the ongoing FIREFLY-1 (NCT04775485) phase 2 study (Kilburn LK, et al. Nat Med. 2023) in this population showed clinically meaningful tumor responses and a manageable safety profile. METHODS: Patients in FIREFLY-1 treated for ≥26 cycles (∼24 months) who entered a DH period were routinely assessed every 3 cycles; once-weekly tovorafenib 420 mg/m2 (not to exceed 600 mg) could be restarted if there was radiographic and/or clinical evidence of new disease progression. RESULTS: As of the April 19, 2024 data cutoff, 26 patients (BRAF fusion: 22; BRAF V600E mutation: 4) (33.8%) of 77 patients in arm 1 (pLGG registrational) had completed 2 years of treatment and started a DH. No patients on a DH withdrew. Twenty-four patients (92.3%) remain on a DH, of which 22 were evaluable for response (duration range: 0.6-10.9 months); duration of response off-treatment ranged from 0.0-8.5 months. (Ranges exclude 2 nonevaluable patients treated beyond radiographic progression who remained on treatment in first 26 cycles due to ongoing clinical benefit; both remain on DH without clinical progression.) Two patients had tumor progression while on a DH and restarted treatment ; 1 patient with a BRAF V600E mutation progressed (≥25% in tumor size) after 1 month (rebound growth per O'Hare P., et al. Neuro-Oncol. 2024: ≥25% increase [per RANO-LGG] w/in 6 months of stopping treatment) and has been on retreatment for 4 months; 1 patient with a BRAF fusion progressed after 9 months and has been on retreatment for 3 months. Treatment-related adverse events of any grade experienced by patients on retreatment were alopecia and rash (1 each). Independent radiographic analysis for response during retreatment is ongoing. CONCLUSIONS: Tovorafenib provided durable tumor responses offtreatment in patients with r/r pLGG on a DH in FIREFLY-1.