LGG-16. TO BE PRECISE - KNOW YOUR TARGETS: INSTITUTIONAL EXPERIENCE WITH TUMOR TARGETED THERAPY FOR RECURRENT/PROGRESSIVE PEDIATRIC LOW-GRADE GLIOMA AND PLEXIFORM NEUROFIBROMA

INTRODUCTION: The oncogenic drivers of pediatric CNS tumors are rapidly being identified with the implementation of high throughput genetic screening. Precision medicine approaches to treatment have shown promising results, but data remains limited in the community oncology setting. We aim to describe our institutional experience using targeted therapies for plexiform neurofibroma and recurrent/progressive pediatric low-grade glioma (pLGG). METHODS: We performed a retrospective chart review of all patients treated with tumor targeted therapies for recurrent/progressive pLGG and plexiform neurofibroma over the past 5 years. RESULTS: Ten patients treated with tumor targeted therapies were identified. Regimens included combination Dabrafenib and Trametinib (n=3), Trametinib monotherapy (n=2), Selumetinib (n=3), Vemurafenib (n=1), and Larotrectinib (n=1). Median age at therapy initiation was 11.5 years (range 1.1 - 18 years). Tumor molecular status included BRAFV600E mutation (n=4), NF1 mutation (n=2), KIAA1549-BRAF fusion (n=1), NACC-NTRK fusion (n=1), and FGFR1 mutation (n=1). Patients trialed an average of 2 treatment regimens prior to targeted therapy initiation (range 0–5). Mean duration of therapy was 14.5 months (range .5–33 months) with 8 patients remaining on treatment. Based on modified RANO criteria, responses included partial (n=1), stable disease (n=8), and progressive disease (n=1). Progressive disease was noted after 4 months of treatment with Dabrafenib and Trametinib combination therapy, but rate of tumor growth was decreased. Subjective functional improvement was seen in 50% of patients. The most common toxicities included rash (n=5) and pyrexia (n=2). Trametinib was discontinued in one patient due to intra-tumoral hemorrhage of unclear etiology. CONCLUSION: Treatment of pediatric CNS tumors with targeted agents appears to be feasible and efficacious in the community oncology setting. Multi-institutional clinical trials are currently ongoing for each of these therapies. There remains a need for community oncology institutional data regarding their use.