Single center experience of IDH inhibitors in high-grade gliomas.

e14036 Background: IDH inhibitors have shown to improve progression free survival in low grade gliomas. Antitumor effect in high-grade gliomas is not well known, with conflicting views regarding the role of IDH mutations in high-grade gliomas and the potential for resistance to DNA-damage-inducing therapies. We present the outcomes of high-grade gliomas that were treated in our institution with IDH inhibitors. Methods: We performed a retrospective review of patients with gliomas treated with FDA approved IDH inhibitors (ivosidenib and enasidenib) in the past 5 years at our institution (January 1 st 2019- January 1 st 2024). Our search identified 32 patients of which 11 were identified as high-grade gliomas (both oligodendrogliomas and astrocytomas). Institutional Review Board PA17-0222 was used for this study. Results: Eleven high grade, IDH-mutant glioma patients treated with IDH inhibitors were identified with a median age at diagnosis of 31 years; 63.6% of these patients were men. Over 63% of patients were categorized as WHO grade 3 and 36.4% as grade 4 tumors. Over 63% of patients were astrocytoma (4 out of 7 patients with WHO grade 4 astrocytoma) while the rest were oligodendrogliomas. All patients underwent initial resection and had received radiation plus at least one prior line of systemic therapy prior to starting an IDH inhibitor. Over 72% were started on IDH-inhibitor therapy after 3 or more recurrences; previous lines of systemic therapy included temozolomide, bevacizumab, and lomustine. Five patients were treated with more than 1 cycle of IDH inhibitor, 2 patients with 8 cycles, and 1 patient with 18 cycles. Of the 11 treated patients, four had progression while on an IDH inhibitor, of which one patient died. IDH inhibitors were discontinued in two patients (due to headaches and abnormal liver enzymes). Median survival and progression free survival after IDH inhibitors were not reached. Conclusions: IDH inhibitors were started on patients with high-grade astrocytoma and oligodendroglioma after multiple recurrences and after receiving DNA-damage-inducing therapies. Prolonged responses were observed in 3 patients (one oligodendroglioma and two WHO grade 3 astrocytomas). Further investigation is needed to establish the role for IDH inhibitors in the treatment of high-grade gliomas.