• 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 neurocognitive examination and the QOL

• Karnofsky performance status ≥ 60

• Laboratory values obtained between 21 days before inclusion andrandomization, respecting the following criteria:

• Absolute neutrophil count (ANC) ≥1500 /mm3

• Platelet count ≥100,000 / mm3

• Hemoglobin \> 9.0 g/dL

• Total bilirubin ≤ 1.5 x upper limit of normal (ULN)

• SGOT (AST) ≤ 3 x ULN

• Negative serum or urine pregnancy test done ≤ 7 days prior to registration, for women of childbearing potential only.

• Provide informed written consent