IDH1 and oligodendroglioma: A recent systematic review and meta‐analysis of the prognostic value of chromosomal 1p/19q codeletion in CNS WHO Grade 2 and 3 oligodendrogliomas found a summary hazard ratio (HR) for mortality of 0.28 (95% confidence interval [CI] 0.13 to 0.62; 9 studies) favouring 1p/19q codeletion after adjusting for age, extent of resection, IDH mutation and type of therapy [16].