BIOM-42. RESPONSE TO DABRAFENIB/TRAMETINIB IN A PATIENT WITH WHO-CNS GRADE 3 BRAF V600E-MUTATED PLEOMORPHIC XANTHOASTROCYTOMA

Abstract BACKGROUND Pleomorphic xanthoastrocytoma (PXA) is a rare central nervous system tumor. Mutations in BRAF V600E are present in 60-80% of cases. While traditionally managed with surgical resection and adjuvant radiation, emerging evidence suggests targeted therapies may be effective, particularly in cases harboring the BRAF V600E mutation. CASE SUMMARY A 35-year-old male with no significant medical history presented in November 2023 with diplopia and headache leading to the discovery of a large left temporal/parietal tumor. A partial resection was performed. Initial histopathological diagnosis was glioblastoma (GBM); thus, the patient was treated with concurrent radiation and temozolomide for 6 weeks. Molecular pathological analysis demonstrated the presence of BRAF V600E mutation and CDKN2A/B copy number loss. Methylation-based tumor profiling was performed at the National Cancer Institute, with composite methylation profile indicating a consensus match to pleomorphic xanthoastrocytoma. Following chemoradiation, a repeat brain MRI in March 2024 showed tumor progression, prompting the initiation of dabrafenib and trametinib therapy. After 1 month of targeted treatment, a repeat brain MRI demonstrated a partial response with a decrease in tumor size and enhancement. In April 2024, he underwent a planned repeat resection. Symptomatically, the patient experienced intermittent headaches and nausea that were responsive to oral steroids with no serious adverse effects to targeted therapy. DISCUSSION This case highlights the therapeutic potential of double BRAF/MEK blockade with dabrafenib and trametinib in BRAF V600E-mutant anaplastic PXA. The observed partial response on imaging suggests the efficacy of targeted therapy in this molecular subtype. These findings underscore the importance of molecular profiling in guiding treatment decisions.