LGG-49. SAFETY AND EFFICACY OF TRAMETINIB (T) MONOTHERAPY AND DABRAFENIB + TRAMETINIB (D+T) COMBINATION THERAPY IN PEDIATRIC PATIENTS WITH BRAF V600-MUTANT LOW-GRADE GLIOMA (LGG)

BACKGROUND: Children with BRAF V600-mutant LGG have suboptimal response to standard chemotherapy. Previously, D (BRAF V600 inhibitor) monotherapy has demonstrated clinical benefit in this population. We report interim analysis results of pediatric patients with recurrent/refractory BRAF V600-mutant LGG treated with either T (MEK1/2 inhibitor) monotherapy or D+T combination therapy. METHODS: This is a 4-part, open-label, multicenter, phase I/II study (NCT02124772) in pediatric patients (<18 y) with refractory/recurrent tumors. The dose-finding phase, including dose confirmation stratified by age, was followed by disease-specific cohorts at recommended dose levels. Efficacy was determined by both investigator and independent review using RANO criteria. Adverse events (AEs) were assessed per NCI-CTCAE v4.03. RESULTS: Of 49 pediatric patients with BRAF V600-mutant LGG (T, n=13; D+T, n=36) enrolled, pooled efficacy data was available for both treatments while safety data was available for 30 patients (T, n=10; D+T, n=20). Most patients (n=8/10) receiving T monotherapy withdrew/discontinued the treatment in contrast to 3/20 in the D+T group. Pyrexia occurred in 50% of patients (n=5/10) in the monotherapy group and was a frequent AE in the combination group (75%; n=15/20). Objective response rate per independent review was 15% (95% CI, 2%–45%) with T monotherapy and 25% (95% CI, 12%–42%) with D+T combination therapy. Seven patients (54%) on monotherapy and 33 patients (92%) on combination therapy had stable disease or better. CONCLUSION: In pediatric patients with previously treated BRAF V600-mutant LGG, T monotherapy and D+T combination therapy demonstrated clinical activity, with pyrexia being a common AE.