Abstract 5137: BRAF mutations in primary central nervous system tumors

Abstract Background: BRAF alterations are present in a variety of primary central nervous system (CNS) tumors from 3% in glioblastomas to 60% in pleomorphic xanthoastrocytomas. BRAF V600E mutation is the most common BRAF alteration found in tumors and has been successfully targeted by combining BRAF/MEK inhibitors in different tumor types, including gliomas. We aimed to describe the clinical and genomic features of primary CNS tumors harboring BRAF alterations and real-world data on BRAF-targeted therapy including our experience sequencing BRAF-directed therapies (BDI) in gliomas. Methods: Single-center retrospective analysis of patients with diagnosis of primary CNS tumors with NGS testing. Clinical, histological and molecular characteristics were analyzed. Results: 44 patients with BRAF mutant primary CNS tumors were included, 28 (64%) were male. 24 (55%) had histology consistent with high-grade glioma (HGG), 14 (32%) low grade glioma (LGG), 4 (9%) low grade neuroepithelial tumors and 2 (4%) others. Missense mutations were found in 77%, followed by amplifications (9%), fusions (9%) and in/del alterations (5%). V600E was the most common mutation (63%), followed by class 2 (16%) and 3 (7%) mutations and amplifications (9%). Co-occurring mutations were found in CDKN2A/B (22), TERT (20) and MTAP (12), median TMB was 2 mut/mb and only 2 patients had high TMB. 4 patients had commuted IDH1 (3 R132H), non-concurring with a V600E mutation. For patients with HGG, median age at diagnosis was 47 years and 16 (66%) were male. Lesions were more frequent in left hemisphere (70%) and temporal lobe (54%). V600E was found in 50% of cases, KIAA1549-BRAF fusion was found in 1 case. Median follow-up was 40 months (95% CI 11-68) and median overall survival (OS) was 22 months (3. 4-40) for the whole population, and 56 (4-109) months for patients treated with BDI (n=4). All 4 patients had an OS 30 months. In the LGG cohort, median age at diagnosis was 34 years (IQR 24-46), 8 (57%) were male. 50% of the lesions were in the left side and 21% of the tumors were in the posterior fossa. 78% had a V600E mutation, with no statistical difference with HGG cohort (p=. 082). Median follow up was 11 months, median OS was not reached. For 5 patients treated at recurrence with BDI, median PFS was 15 months (3-27). 5 patients were treated with plixorafenib (PLX8394) on clinical trial achieving disease control (PR +SD) in 4 cases. Upon progression, 4 were rechallenged with dabrafenib + trametinib and 1 with another BDI. 4 patients had a partial response with duration of response 6 months in 3 cases. Conclusion: BRAF mutant CNS tumors are a heterogeneous disease. Longer survival was observed in the small group of HGG patients treated with BDI compared to SoC (56 months vs 22months). BDI rechallenge showed durable responses in heavily pretreated patients. Further molecular characterization of these patients is ongoing. The best therapeutical sequencing strategy for BDI remains uncertain. Citation Format: Juan B. Blaquier, Fulvio D'Angelo, Dalissa Tejera, Ruham A. Nasany, Gaurav Saigal, Antonio Iavarone, Macarena I. de la Fuente. BRAF mutations in primary central nervous system tumors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5137.