Pseudoprogression is defined as an increase in enhancement and/or T2/FLAIR signal abnormality on MRI within 12 weeks of radiotherapy or combined radiotherapy-chemotherapy, with spontaneous resolution or stabilization without change in management, occurring in 15–50% of patients with gliomas (MGMT-methylated and IDH-mutant tumors especially) [136]. The gene discussed is IDH1; the disease is glioma.