P12.23.B IDH INHIBITION AT RELAPSE?

Abstract BACKGROUND IDH mutant gliomas constitute a heterogeneous group of primary malignant brain tumors, whose prognosis may vary depending on their molecular characteristics and degree of differentiation. For many decades, in addition to surgical resection, observation or the administration of radiotherapy alone or in combination with chemotherapeutic agents have been the mainstay of treatment. In recent years, the encouraging results with IDH targeting led to the approval of vorasidenib, as adjuvant treatment in patients with resected grade II disease. Nonetheless patients do relapse, many of whom have never received an IDH inhibitor and the question remains regarding the efficacy of these agents in the relapsed setting. MATERIAL AND METHODS We have collected data from our patients who have received treatment with ivosidenib in settings that didn’t include the indication of vorasidenib, with the aim of investigating its effectiveness mainly in previously treated patients. RESULTS From 20/05/2024, 6 patients with IDH mutated glioma have already received treatment with ivosidenib at our oncology center. The median age of diagnosis was 29 years old. At initial diagnosis, 2 patients had an astrocytoma gr 2, 2 patients with oligodendroglioma gr3, 1 patient with astrocytoma gr3 and 1 patient with a pontine glioma without histologic diagnosis. Apart from one patient who was diagnosed with astrocytoma gr 3 in 12/2022 and who only received ivosidenib for 48 days and died from the disease, the other 5 patients are still on treatment. The median duration on treatment is 133 days, with the first patient to receive the drug already being under treatment for 316 days. Regarding the imaging response, 4 patients have stable disease while 1 patient has a partial response. All the patients that are still under treatment have clinical stability or improvement without experiencing any adverse effects. CONCLUSION In this small patient series, ivosidenib appears to be a well-tolerated therapeutic option and with satisfactory efficacy in previously treated patients with IDH mutated gliomas. Despite some discouraging existing data with this agent in the advanced setting, further testing of the efficacy of IDH inhibition beyond the adjuvant setting may be warranted.