HOUT-23. SEIZURES IN GRADE III GLIOMAS: NATURAL HISTORY AND RESPONSE TO TREATMENTS

There is lack of studies focused specifically on seizures in grade III gliomas in the MRI and molecular genetics era. The aim of this retrospective study was to describe the natural history and response to treatments of seizures in a cohort of grade III gliomas taking into account the molecular markers. We retrieved from our institutional database all patients with grade III astrocytoma, oligodendroglioma and oligoastrocytoma according to WHO 2007 with at least one seizure in the disease course, who were followed between 1995 and 2015. We evaluated seizure type, frequency, and control after surgery, radiotherapy, chemotherapy and chemoradiation. We found 133 patients with grade III glioma of whom 91 de novo and 42 from previous grade II tumors. Overall, seizures were the presenting symptom in 88% of patients, while occurring later in 12%, and were simple partial (54%), partial complex (13%) and secondary generalized (19%). Seizure frequency was ≥ 1/day in 5% patients, and tumors with IDH1/2 mutations showed a higher seizure frequency (≥ 1 seizure/day in 9%) than grade III IDH1 wild-type (≥ 1 seizure/day in 0%). After surgery 70% of patients were seizure free, and a seizure reduction ≥50% was observed in 61% following radiotherapy, 52.4% following TMZ or PCV, and 38% following chemoradiation. Patients with both IDH1/2 mutations and 1p19q codeletion showed a better seizure reduction (71% after radiotherapy and 64% after chemotherapy) than those with IDH1/2 wild type (60% after radiotherapy and 38% after chemotherapy, p˃0.01). This study confirms the high epileptogenicity of grade III gliomas, and suggests that adjuvant antineoplastic treatments may favorably impact seizure control. To our knowledge, this is the first study reporting that IDH1/2 mutated grade III gliomas have a higher seizure frequency but a better seizure control after antineoplastic treatments than IDH1 wild-type tumors.