CTNI-37. CLINICAL ACTIVITY OF RAF INHIBITOR TOVORAFENIB ACCORDING TO PRIOR MAPK INHIBITOR TREATMENT IN THE REGISTRATIONAL PEDIATRIC LOW-GRADE GLIOMA ARM OF THE PHASE 2 FIREFLY-1 (PNOC026) STUDY

Abstract BACKGROUND Pediatric low-grade glioma (pLGG) is the most common childhood brain tumor. Genomic alterations of RAF are common oncogenic drivers in pLGG. Tovorafenib is an investigational, selective, CNS-penetrant, type II RAF inhibitor. METHODS FIREFLY-1 (NCT04775485) is a phase 2 study evaluating tovorafenib monotherapy. Registrational arm 1 enrolled patients aged 6 months–25 years of age with recurrent or progressive LGG harboring an activating BRAF alteration. Tovorafenib 420 mg/m2 (600 mg max) was administered weekly (tablet or liquid suspension). Independently assessed overall response rate (ORR), as defined by RANO-HGG and RANO-LGG criteria, are primary and exploratory endpoints. RESULTS As of December 22 2022, 69 (RANO-HGG) and 76 (RANO-LGG) of 77 patients in arm 1 were evaluable at baseline and had ≥9 months of follow-up. Median age at enrollment was 8 years (range 2–21), and 60% (n = 46) patients had received prior MAPK inhibitor (MAPKi) therapy. Among the evaluable patients, the ORR was 62% (RANO-HGG, n = 69) and 45% (RANO-LGG, n = 76), respectively. The ORR in patients previously treated with MAPKis (n = 41 [RANO-HGG]; n = 45 [RANO-LGG]) was 68% (4 CRs; 24 PRs) (RANO-HGG) and 44% (5 PRs; 15 MRs) (RANO-LGG). In MAPKi-naïve patients (28 [RANO-HGG]; 31 [RANO-LGG]), the ORR was 54% (15 PRs) (RANO-HGG) and 45% (7 PRs; 7 MRs) (RANO-LGG). Among 136 patients in arms 1 and 2 of FIREFLY-1, the most common treatment-related adverse events (TRAEs) of any grade were hair color changes (71%), fatigue (40%) and maculopapular rash (38%). Tovorafenib dose modifications occurred in 39 (29%) and discontinuations in 4 (3%) patients due to TRAEs. CONCLUSIONS Tovorafenib provided clinically meaningful tumor responses, including those with a best response reported of SD or PD using another MAPKi, in patients with BRAF-altered pLGG regardless of prior MAPKi therapy, and has a manageable safety profile.