Molecular alterations to predict survival and response to chemotherapy of pediatric low-grade glioma.

Abstract

10503 Background: RAS/MAPK pathway mutations have been identified as the major drivers of pediatric low-grade glioma (pLGG). The impact of these alterations on outcome and response to therapy is still unknown. Methods: We performed a large population based study of all pLGG diagnosed from 1985-2015. Detailed treatment and very long term outcome data was collected on all patients. Known pLGG-related alterations were detected using NanoString and QX200™Droplet Digital™PCR. Molecular data was correlated with outcome and response to chemotherapy. Results: In our cohort of 614 patients, BRAF was found to be altered in 57% and wild-type (WT) in 43% of patients without neurofibromatosis 1 (NF1). Among BRAF-WT we identified H3.3K27M, FGFR1-TACC1, MYBL1 and other alterations. Molecular alterations stratified pLGG into several risk groups. Ten-year progression free survival (PFS) was 72.3% for NF1, 69.5% for KIAA1549-BRAF, 53.5% for BRAF-WT, 30.3% for BRAF-V600E and 0% for H3.3K27M mutations (p < 0.0001). Similarly, overall survival (OS) at 10 years delineated difference between excellent survival of KIAA1549-BRAF and NF1 compared to BRAF-V600E and BRAF-WT (p = 0.0005). Interestingly, all patients with FGFR1-TACC1 and MYBL1 were alive despite observed progressions. Strikingly, response to chemotherapy determined by changes in tumor size at 6 months of therapy correlated with pLGG alteration. Objective response to first line chemotherapy was observed in 46% of patients with KIAA1549-BRAF and 35% of NF1. In contrast, only 15% BRAF-V600E and 18% BRAF-WT responded and 41% tumors grew after six months of chemotherapy. Moreover, 5-year PFS after chemotherapy was strikingly low for BRAF-V600E and BRAF-WT (25% and 31.9% respectively) compared to KIAA1549-BRAF (50%) and NF1 (76.7%) (p = 0.001). This translated to decreased OS for BRAFV600E and BRAF-WT patients (p = 0.042). Conclusions: Our study provides evidence that molecular alterations dictate the outcome of pLGG. KIAA1549-BRAF harbors excellent prognosis and choice of therapy should be made in favor of less toxic agents to minimize deleterious late effects. In contrast, poor prognosis is associated with lack of response to chemotherapy in BRAF-V600E and BRAF-WT tumors.