PROGNOSIS OF IDH-MUTANT ADULT LOW-GRADE GLIOMA IN THE MODERN ERA

Abstract AIMS Since 2016, the standard oncological treatment of high-risk adult diffuse IDH-mutant low-grade gliomas (LGG) after initial surgery has changed from the sole use of radiotherapy (RT-alone) to the combined use of radio- therapy and chemotherapy (RT+CT). This study aimed to determine the uptake and effectiveness of RT+CT in a real-world environment by comparing survival and seizure outcomes in two cohorts treated in a single centre, pre- and post-2016. METHODS Retrospective collection of adult patient data diagnosed with IDH-mutant LGG treated at University College London Hospitals from 2009-2015 (Group 1) and 2016-2022 (Group 2). The Progression-Free Survival (PFS), Overall Survival (OS), and seizure outcomes of the two cohorts were analysed. RESULTS 78 patients were treated in Group 1 and 79 in Group 2. There were more Complete Resections in Group 2 com- pared with Group 1 (53% vs 19%). As expected, more patients were treated with RT+CT in Group 2 than Group 1 (25% vs 10%) and vice versa for RT-alone (45% vs 10%). RT+CT led to a significant increase in PFS (3.2 vs 7 years, p=0.02) but not OS compared with RT-alone. PFS was longer in Group 2 patients with oligodendrogliomas (but not astrocytomas) compared with Group 1 (median not reached vs 6.4 years), with the survival curves diverg- ing at 3 years. PFS was significantly greater in the RT+CT patients who had Biopsy-only compared with those who had Partial/Complete Resections. No significant differences were found in seizure occurrence/frequency between the two groups. CONCLUSION RT+CT improved PFS but not OS or seizure outcomes in patients with IDH-mutant oligodendrogliomas and pa- tients who had Biopsy-only. Given the long natural history of these tumours, it has not yet been possible to demonstrate improvements in OS. Patients with astrocytomas who had Partial/Complete Resections could be potentially spared from the additional CT noting the adverse effects and insignificant survival benefits.