A Randomized Trial of Delayed Radiotherapy in Patients Low-grade Oligodendrogliomas Requiring a Treatment Other Than Surgery

Inclusion Criteria: * Tumor is co-deleted for 1p and 19q based and IDH-mutant (IDH1 or IDH2) according to local diagnosis * Histological confirmation of low-grade oligodendroglioma by central pathological review according to WHO 2016 classification * Age ≥ 18 years * Patients with one or several prior surgical procedure for a low-grade oligodendroglioma and who undergo a resurgery are eligible if they have not received prior radiotheray or chemotherapy and if the last histological diagnosis is a low-grade oligodendroglioma prior use of specific HDI prohibitions is permitted * Patients who undergo an initial follow-up after surgery or re-surgery are eligible if there is no evidence of anaplastic transformation on MRI (no new contrast enhancement, no obvious modification of the growth rate) * Patients requiring an oncological treatment other than surgery because of one or more of the following characteristics: * Progressive disease defined as documented growth prior to inclusion * Symptomatic disease defined as the presence of neurological or cognitive symptoms or refractory seizures defined as having both persistent seizures interfering with everyday life activities other than driving a car and three lines of anti-epileptic drug regimen had not worked, including at least one combination regimen. * Age ≥ 40 and any surgical therapy * Age \< 40 with prior and subtotal resection or biopsy (i.e., anything less than gross total resection) * Willing and able to complete ne…