NIMG-57. NON-INVASIVE DIAGNOSIS OF IDH-MUTANT BRAINSTEM GLIOMAS

Abstract INTRODUCTION Treatment of brainstem tumors is often initiated without a tissue diagnosis due to the risk biopsy. A subset gliomas harbor an isocitrate dehydrogenase 1/2 (IDH) mutation, which predicts response alkylator chemotherapy and IDH inhibitors; non-invasive diagnostic tests are needed identify these mutations. METHODS We identified cohort patients with IDH-mutant through chart review who underwent magnetic resonance spectroscopy (MRS) and/or brain mutation was established by biopsy, presence 2-hydroxyglutarate (2HG) peak on MRS, or identification cerebrospinal fluid (CSF) sequencing cell-free DNA (cfDNA). RESULTS 15 gliomas, age range 5-48, 47% women. 15/15 were involving/abutting brachium pontis, 10/15 non-enhancing at diagnosis. 13/15 1/15 MRS CSF, only. 10/13 available data had non-IDH1 R132H in IDH1/2. 7/7 prior radiation 2HG (MRS concordant all cases biopsy obtained). 4/6 post-radiation retained peak. 4 cfDNA found 2/4. Response patients; received radiation, 10 concurrent temozolomide: best partial 8 stable disease 5. inhibitor: 2 after progression, as maintenance radiation/temozolomide, achieving tumor control all. For this cohort, median PFS 71.4 months OS has not been reached. CONCLUSION have characteristic appearance, high rate treatment, better overall prognosis than other tumors. CSF allow for mutations patients.