3. Glioma: Updated classification, immune biomarkers, and therapeutic approaches
3.1 Diagnosis and classification
Gliomas are the most common and varied tumours originating from the central nervous system (CNS) parenchyma. When reviewing the literature on glioma it is important to acknowledge changes in their classification (and clinical diagnosis) over time (Figure 3). Since the 2016 WHO CNS tumour classification (revised 4th edition)63,64, particular molecular alterations are part of the definition of multiple gliomas, including adult-type diffuse gliomas. These latter tumours are characterized by extensive infiltration of tumour cells in the surrounding CNS parenchyma and constitute the bulk of adult neuro-oncology practice. The taxonomy of adult-type diffuse gliomas is now largely based on the presence/absence of a hotspot mutation in isocitrate dehydrogenase gene 1 or 2 (IDH1 or IDH2) and of combined, complete loss of the short arm of chromosome 1 and of the long arm of chromosome 19 (1p/19q codeletion). In the 2021 or 5th edition of the WHO CNS tumour classification10 three tumour types are recognized in this family: diffuse astrocytoma, IDH-mutant (grade 2, 3 or 4); oligodendroglioma, IDH-mutant and 1p/19q-codeleted (grade 2 or 3); and glioblastoma, IDH-wildtype, which is not only the most malignant (grade 4), but also the most frequent in adults. Elucidation of molecular differences between adult- and paediatric-type diffuse gliomas has allowed for recognizing these as distinct groups of tumours. The 2021 WHO classification now lists (next to adult-type diffuse gliomas) a family of low-grade and high-grade paediatric-type diffuse gliomas (Supplementary Table 1).
Figure 3: WHO classification of gliomas over time.