LGG-17. CLINICAL OUTCOME OF PEDIATRIC LOW GRADE GLIOMA WITH POSITIVE BRAF-FUSION TREATED WITH MEK INHIBITOR

BACKGROUND: Low grade glioma (LGG) is the most common central nervous system (CNS) tumor in children. Some are treated with surgery alone, while chemotherapy is given for unresectable tumor with clinical symptoms or progression. Conventional chemotherapy is effective but 30–40% patients may have reactivation of disease requiring re-treatment throughout lifetime. MEK inhibitor for BRAF-fusion positive LGG is a new treatment option for refractory cases. METHODS: Retrospective search in territory-wide pediatric oncology registry for children diagnosed with LGG from 2010–2020 in Hong Kong. To identify patients with molecular confirmed BRAF-fusion positive LGG and any treatment with MEK inhibitor. RESULTS: Twelve patients (N=12) were identified with BRAF-fusion positive LGG, male:female was 1:2, age 0.3–15.1yr (median 5.0yr) at presentation. The median follow up duration was 1.8yr. Five patients (42%) had surgical resection only. Seven patients (58%) were given chemotherapy with Carboplatin / Vincristine. Five out of seven (n=7) treated patients (71%) have partial response at their initial treatment. Two patients (29%) had progressive disease during treatment and switched to second-line chemotherapy, vinblastine however without improvement. Three patients required re-treatment as disease reactivation. Total five patients had refractory diseases were treated with MEK inhibitor, Trametinib including one diagnosed NF-1. All of them have adverse skin reaction and raised transaminase with one required dose reduction. They have been taking the MEK inhibitor for 0.1–3.3 yr with sustainable partial response. CONCLUSION: Pediatric LGG has overall favourable prognosis. Some of them treated with surgery alone while conventional chemotherapy could also achieve satisfactory disease control. For refractory disease with BRAF-fusion positive, MEK inhibitor is a well tolerated treatment option showing sustainable partial response. However, prolonged medication and disturbing skin reaction are still a major concern for this group of patients. On-going clinical trials to compare conventional chemotherapy versus MEK inhibitor could give us more insight about the clinical benefit, patient selection and treatment duration.