CLINICAL ACTIVITY AND SAFETY OF THE RAF INHIBITOR TOVORAFENIB IN PATIENTS WITH OPTIC PATHWAY GLIOMAS IN THE REGISTRATIONAL PEDIATRIC LOW-GRADE GLIOMA ARM OF THE PHASE 2 FIREFLY-1 (PNOC026) STUDY

Abstract

BACKGROUND: Optic pathway gliomas (OPG) are low-grade gliomas (LGG) comprising 3-5% of pediatric brain tumors. Morbidity may include visual loss (acuity and visual fields), hypothalamic/pituitary dysfunction, and/or impaired motor function. Genomic alterations of MAPK/BRAF are frequent oncogenic drivers in pediatric LGG. Activity of tovorafenib, an investigational, oral, selective, CNS-penetrant, type II RAF inhibitor in OPGs was analyzed. METHODS: FIREFLY-1 (NCT04775485) is a phase 2 study evaluating tovorafenib (420 mg/m2 weekly) in patients 6 months-25 years with BRAF-altered recurrent/progressive LGG or solid tumors. Independently assessed overall response rate (ORR), as defined by RANO-HGG and RANO-LGG criteria, are primary and exploratory endpoints. RESULTS: Of the 77 patients enrolled in arm 1 (measurable disease per RANO-HGG), 42 (55%) had tumors located in the optic pathway. Median age at enrollment was 8 years (range: 2-16); 37 (88%) harbored a BRAF fusion and 5 (12%) a BRAF V600E mutation. The median prior lines of systemic therapy was 3 (range: 1-9), with 69% having received prior MAPK inhibitors. Of the 39 evaluable patients (RANO-HGG), the ORR was 59% (1 CR, 22 PRs) with a median time to response (TTR) of 2.8 months; 14 (36%) had stable disease (SD). Per RANO-LGG (n = 42), the ORR was 43% (5 PRs; 13 MRs) with a median TTR of 4.1 months; 20 (48%) had SD. Visual acuity remained stable in 79% (23) of patients (Cycle 9, n = 29 assessed). The most common treatment-related adverse events (TRAEs) of any grade in this subgroup were hair color changes (81%), increased creatine phosphokinase (55%), anemia (48%), maculopapular rash (45%), and fatigue (41%). Dose modifications occurred in 14 (33%) and discontinuations in 3 (7%) patients due to TRAEs. CONCLUSIONS: Tovorafenib demonstrated antitumor activity in recurrent/progressive BRAF-altered OPG and was generally well tolerated. Visual acuity remained stable for the majority with OPGs.