Clinical activity of pan-RAF inhibitor tovorafenib in the registrational pediatric low-grade glioma arm of the phase 2 FIREFLY-1 (PNOC026) study.
Authors: Kilburn Lindsay Baker , Khuong-Quang Dong-Anh , Nysom Karsten , Landi Daniel B , Ziegler David Simon , Hernáiz Driever Pablo , Leary Sarah , Bailey Simon , van der Lugt Jasper , Perreault Sébastien , Waanders Angela Jae , Baxter Patricia Ann , Witt Olaf , Hargrave Darren R. , McCowage Geoffrey Brian , Zhao Xin , Da Costa Daniel , Cox Michael Craig , Manley Peter , Hansford Jordan 
Published: June 2023

10004 Background: Pediatric low-grade gliomas (LGGs) are the most common brain tumors of childhood. Genomic alterations of BRAF ( KIAA1549-BRAF fusions, 50–60% and BRAF V600E mutations, 5–15%) are the most frequent oncogenic drivers in pLGGs. Tovorafenib is an investigational, oral, selective, brain-penetrant, small molecule, type II pan-RAF inhibitor. Tovorafenib has demonstrated clinically meaningful responses in 24/35 patients (2 CR, 7 PR and 15 SD) in the pediatric phase 1B PNOC014 (NCT03429803) trial in patients with RAF-altered cancers (Wright, SNO 2022). Methods: FIREFLY-1 (NCT04775485) is a multicenter phase 2 study evaluating the efficacy and safety of tovorafenib monotherapy in patients with BRAF-altered cancers. Registrational arm 1 of FIREFLY-1 includes patients 6 months–25 years of age with recurrent or progressive LGG previously treated with ≥1 prior line of systemic therapy. Tovorafenib 420 mg/m2 (not to exceed 600 mg) is administered weekly, in 28-day cycles, (tablet or liquid suspension formulation) until progression. The primary endpoint of arm 1 is ORR, as defined by Response Assessment in Neuro-Oncology (RANO) criteria and determined by blinded independent review. Results: As of September 28, 2022, arm 1 had enrolled 77 patients and is fully accrued. All patients had ≥6 months of follow-up. Median age at enrollment was 8 years (range 2–21). Patients were pretreated with a median of 3 prior lines of systemic therapy (range: 1–9); 60% had received prior MAPK pathway-targeted agents. The most common tumor site was optic pathway (51%). Sixty-four patients harbored a BRAF fusion/rearrangement (83%) in their tumors, and 13 (17%) had a BRAF V600E mutation. Median duration of tovorafenib treatment is 8.4 months (range 0.7–16.8), with 59 patients (77%) remaining on treatment at the time of data cutoff. Per independent assessment in 69 RANO-evaluable patients, ORR was 64%, [3 CR, 41 PR (10 unconfirmed) and 19 SD] with a clinical benefit rate of 91%. Responses were achieved in tumors with BRAF fusions and V600E mutations, including those previously treated with MAPK inhibitors. The most common treatment-related adverse events (TRAEs) of any grade were hair color changes (75%), increased creatine phosphokinase (64%), anemia (46%), fatigue (42%) and maculopapular rash (42%). Tovorafenib dose modifications occurred in 16 (21%) and discontinuations in 2 (3%) patients due to TRAEs. Updates from a longer follow-up on the 77 patients in arm 1 will be presented at the meeting. Conclusions: Tovorafenib was generally well tolerated and showed encouraging evidence of antitumor activity in children and young adults with recurrent/progressive BRAF-altered pLGG. LOGGIC/FIREFLY-2 (NCT05566795), a global, phase 3 trial is evaluating once-weekly tovorafenib monotherapy in newly-diagnosed patients with pLGG harboring a known activating RAF alteration. Clinical trial information: NCT04775485 .