LGG-07. IS BRAF ALTERATION OR A HISTOLOGIC ‘QUALIFIER’ A PREDICTOR OF OUTCOME IN PEDIATRIC PILOCYTIC ASTROCYTOMA?

INTRODUCTION: Pediatric pilocytic astrocytomas (PA) are the most common pediatric central nervous system tumor. Surgical resection is the primary treatment for PA with five-year survival rates up to 95%. Despite a favorable prognosis, our understanding about the prognostic value of histopathological findings, such as histopathologic qualifier* or BRAF alterations is evolving. METHODS: Patients treated for a WHO grade 1 PA at Washington University in St. Louis/St. Louis Children’s Hospital were analyzed for clinical details, including pathology diagnosis (*histopathologic qualifier refers to designations in the diagnosis such as “WHO Grade I pilocytic astrocytoma with increased proliferative index”). BRAF alterations include gene fusions and point mutations. RESULTS: 224 patients were analyzed (51% female, mean age 9.6 years). Tumors were located in the cerebellum/fourth ventricle (50%), optic pathway/hypothalamus (15%), brainstem (12%), and cerebral cortex (11%). BRAF alterations were identified in 55/77 patients (71.4%) and additional histopathologic qualifiers were present in 27/220 patients (12.3%). 196 patients (87.5%) underwent surgical treatment and 22 (9.8%) had biopsy alone. 45 patients (22%) displayed tumor progression or recurrence after resection. The presence of a histopathologic ‘qualifier’ in the topline or BRAF alteration was not associated with tumor progression or recurrence (p=0.36, p=0.77). Ki-67 proliferative indices were not predictive of progression or recurrence (p=0.94), including when controlling for extent of resection and adjuvant therapy. BRAF alterations, specifically KIAA1549 fusions, were associated with cerebellar/fourth ventricular tumor location (p<0.001) and younger patient age (p=0.03). Extent of resection was the only predictor of outcome identified in this study; patients with gross total resection had significantly lower rates of progression and recurrence (p<0.0001). CONCLUSION: BRAF alterations and histopathologic qualifiers were not associated with tumor progression or recurrence in pediatric PA, although BRAF fusions were more common in tumors located in the cerebellum/fourth ventricle and in younger patients.