P12.42.a Early [18f]fet Pet-Mri Follow-Up in Idh-Mutant Glioma Patients Treated With Vorasidenib

BACKGROUND The IDH inhibitor vorasidenib has been made available in the Netherlands via a patient access program. Early markers of response would be highly valuable for clinical decision-making but are currently lacking. There is a growing body of evidence that amino acid PET imaging might be helpful. Here, we report on our single-center experience with [18F]FET PET-MRI at baseline and after 3 months of treatment with vorasidenib in patients with IDH-mutant glioma. MATERIAL AND METHODS At the Brain Tumor Center of Erasmus MC Cancer Institute in Rotterdam, [18F]FET PET-MRI is available in routine clinical practice. For patients scheduled to begin vorasidenib treatment, a [18F]FET PET-MRI is performed before the start of therapy, followed by a planned [18F]FET PET-MRI at 3-months. Thereafter, radiological follow-up is performed with MRI, and additional [18F]FET PET-MRI is done on indication. Here, we describe the clinical parameters, [18F]FET-PET changes and MRI-based tumor growth rates before and after start of vorasidenib in patients who had a [18F]FET-PET-MRI and were/are treated through the patient access program. RESULTS Fourteen patients with IDH-mutant glioma underwent a baseline [18F]FET PET-MRI before the start of vorasidenib. At the time of abstract submission, six patients had completed the planned 3-month follow-up [18F]FET PET-MRI, while four were awaiting their scan (data will be available at EANO meeting). Two patients did not have follow-up [18F]FET PET-MRI because there was no metabolic uptake at baseline, and two patients discontinued vorasidenib before the 3-month follow-up due to elevated ALT and AST levels. Among the six patients with a 3-month follow-up [18F]FET PET-MRI, no significant changes in metabolic uptake were observed compared to baseline. Twelve patients are still on vorasidenib treatment at time of abstract submission. Data collection and patient inclusion are ongoing. Tumor metabolic response and growth rate analyses will be presented at EANO. CONCLUSION In this limited sample, no significant changes in metabolic uptake were observed 3 months after the start of vorasidenib therapy. Data collection and patient inclusion is ongoing, and updated results will be presented at EANO.