Histopathological grading affects survival in patients with IDH-mutant grade II and grade III diffuse gliomas

Abstract Background Diffuse grade II and grade III gliomas are actually classified in accordance with the presence of isocitrate dehydrogenase mutation (IDH-mut) and the deletion of both 1p and 19q chromosome arms (1p/19q codel). The role of tumour grading as independent prognostic factor in these group of tumours remains matter of debate. The aim of this study was to determine if grade is an independent prognostic factor and not somehow associated to IDH mutation and 1p/19q status of the tumour. Methods We analysed 399 consecutive patients with newly diagnosed, histologically proven World Health Organisation (WHO) 2016 grade II or grade III IDH-mut gliomas, assessed by polymerase chain reaction, immunohistochemistry or next-generation sequencing (NGS). Results The analysis included 399 patients with grade II (n = 250, 62.7%) or grade III (n = 149, 37.3%) diffuse gliomas. Median follow-up time was 105.3 months. Median survival was 148.1 months. In multivariate analysis, grade II (hazard ratio [HR] = 0.342, 95% confidence interval [CI]: 0.221–0.531; P  Conclusions In our study, histopathological grade still affects survival in IDH-mutant WHO grade II and III diffuse gliomas. This effect appears to be independent from molecular features, extension of surgical resection and post-surgical treatments. Therefore, physicians should continue to take into account tumour grade, along their molecular characteristics, for a better clinical and therapeutic management of the patients.