LGG-52. BINIMETINIB IN CHILDREN WITH PROGRESSIVE OR RECURRENT LOW-GRADE GLIOMA NOT ASSOCIATED WITH NEUROFIBROMATOSIS TYPE 1: INITIAL RESULTS FROM A MULTI-INSTITUTIONAL PHASE II STUDY

Abstract

BACKGROUNDRAS/RAF/MEK/ERK pathway activation is the primary driver for most pediatric low-grade gliomas (LGG). Binimetinib is an orally bioavailable MEK1/2 inhibitor found to have significant central nervous system penetration in a preclinical model.OBJECTIVEThe primary objective of this multi-institutional open-label phase II study was to assess preliminary efficacy of binimetinib in progressive pediatric LGG. The study included strata for both neurofibromatosis type I (NF1) and non-NF1 associated tumors, as well as a target validation (surgical) stratum. NF1 and surgical strata remain open to enrollment and will be reported separately.METHODSChildren aged 1–18 years with previously treated recurrent or progressive LGG were eligible. The dose of binimetinib was 32 mg/m2/dose twice daily. Partial and minor responses were defined, respectively, as 50% and 25% decrease in maximal two-dimensional measurements.RESULTSFifty-seven eligible patients without NF1, median age 8 years, were enrolled and began treatment; 26 were female; 28 had documented KIAA1549-BRAF fusion. Eleven patients discontinued drug in the first year due to toxicity, and an additional 27 required dose reduction. The most common drug-attributable grade 3 toxicities included creatine kinase elevation (n=9 patients), rash (n=8), and truncal weakness (n=8). Truncal weakness improved or resolved with dose reduction or cessation. Grade 4 toxicities included creatine kinase elevation (n=2) and transient colitis (n=1). Of 44 patients with preliminary response data available, 22 (50%) showed a minor (n=7) or partial (n=15) response.CONCLUSIONBinimetinib is active, with manageable toxicities, in children without NF1 with progressive LGG.