161 Pediatric Versus Adult Pilocytic Astrocytoma (PA): Largest Comparison Cohort of Clinical Course & Genomic Profile Demonstrates BRAF-KIAA1549 Fusion is Associated With Worse Prognosis in Children Compared to Adults

INTRODUCTION: Recent work demonstrates significant associations between genomic status and clinical outcomes in pediatric pilocytic astrocytoma (PA). To date, a detailed comparison with adult PA patients has yet to be made. METHODS: We retrospectively reviewed treatment for pediatric and adult PA (2000-2023). BRAF-KIAA1549(B-K) fusion and BRAF-V600E mutations detected through immunohistochemistry, chromosomal-microarray, and next-generation sequencing were identified via pathology records. RESULTS: We identified 315 children (mean age at diagnosis 8.1 years, 50.8% female) and 29 adults (34.5 years, 41.4% female). Most common tumor locations were posterior fossa (59.7% pediatric, 51.7% adult) and suprasellar (21.3% pediatric, 24.1% adult). Pediatrics were more likely to experience obstructive hydrocephalus (p<0.01) necessitating EVD placement (p=0.02). Gross-total resection was achieved in 59.4% pediatric and 48.3% adults (p=0.08). Median length of postoperative stay was shorter in adults (4 versus 8 days, p=0.002). Adjuvant chemotherapy was more common in children (26% versus 3.4%, p=0.013), while adults were more likely to receive adjuvant radiotherapy (27.6% versus 1.3%, p< 0.001). BRAF-V600E mutations were identified in 8/67 children and 1/9 adults (p=0.48); B-K fusions were identified in 44/76 (57.9%) children and 2/10(20%) adults tested (p=0.055). Tumor progression/recurrence occurred in 5 (17.2%) adults and 69(21.9%) children (p=0.65). Median progression/recurrence-free survival (PRFS) time for children and adults was 4.6 and 2.2 years respectively (p=0.81, log-rank test). BRAF-V600E mutation did not confer worse PRFS compared to wildtype in either population. B-K fusion was associated with significantly shorter PRFS in pediatrics (3.0 versus 5.4 years, p=0.036), a trend which was not statistically significant in adults (p=0.2). CONCLUSIONS: This represents the largest cohort comparing genetics/clinical course of pediatric versus adult PA. Rates of obstructive hydrocephalus and adjuvant chemotherapy use were more common in children; radiotherapy was favored for adults. B-K fusions were more frequent in pediatrics and associated with worse PRFS than adults.