Innv-06. Second Generation Braf/Mek Inhibition in Anaplastic Pleomorphic Xanthroastrocytoma

Abstract

BACKGROUND Up to 65% of anaplastic pleomorphic xanthoastrocytomas (A-PXA) harbor the BRAFV600E oncogene. Trials and case series have demonstrated that BRAF-mutant gliomas, including A-PXAs, can be responsive to the first generation BRAF inhibitors dabrafenib and vemurafenib, with an ORR ranging from 26–43%. The second generation BRAF/MEK inhibitor combination encorafenib/binimetinib improves systemic outcome in melanoma patients, has better tolerability, and may have better intracranial activity compared to first generation drugs. METHOD We review the three patients with BRAFV600E A-PXA treated with encorafenib/binimetinib in our practice. RESULTS Two patients were diagnosed with A-PXA in 2014 and one in 2013. The presence of BRAFV600E was confirmed by molecular testing. All patients have received prior surgery, chemotherapy, and radiation and were at a recurrence when BRAF/MEK inhibition was initiated. One patient had CR after 2 months on treatment and remains in CR at 1-year. One patient, who is also receiving bevacizumab, has a PR, with continued clinical and imaging improvement at 6 months. Our third patient had a PR at 2 months and remains on therapy, currently 3 months post-initiation. All 3 patients report improvement in symptoms. The patient who has been on treatment for 1 year experienced rapid onset bilateral multifocal sub-retinal fluid collections followed by rapid resolution, without intervention, within days of starting treatment. This patient has also had mild decrease in EF over time. We will present continued follow up. CONCLUSIONS Encorafenib/binimetinib appears feasible, with 3 of out 3 patients with BRAFV600E A-PXA demonstrating radiographic response; 2 of these patients have durable responses. We stress the importance of a clear lab, cardiac, ophthalmologic, and dermatologic monitoring regimen as side effects can be rapid and severe. Prospective studies with encorafenib/binimetinib in BRAF-mutant primary CNS tumors are underway, and we eagerly anticipate their RESULTS: