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According to the 4th edition of the WHO classification of CNS tumors (2007) [2, 3] the vast majority of gliomas comprises four histological groups, namely astrocytomas, oligodendrogliomas (OD), mixed oligoastrocytomas, and ependymomas, according to their microscopic morphological similarities with the normal cellular counterparts (Table 1). Additionally, this classification presumed histopathological grading of the tumor (WHO grades I–IV). In general, typing of the neoplasm is directed at the recognition of its biological origin, while grading determines a stage in the malignant progression [12].

Nevertheless, the updated WHO classification of CNS tumors (2016) [11] for the first time considers the presence of some genetic alterations in diffuse gliomas, mainly mutations of the isocitrate dehydrogenase 1 and 2 genes (IDH1/IDH2) and combined complete loss of the chromosomal arms 1p and 19q (1p/19q co-deletion), which are incorporated into the lesion name (Fig. 1). Thus for pathological characterization of the neoplasm molecular testing is considered mandatory. If it is not available or cannot be fully performed, an NOS (not otherwise specified) definition is applied. Notably, during establishment of diagnosis for diffuse astrocytic and oligodendroglial tumors the genotype trumps the histological phenotype. Additionally, the updated WHO classification of CNS tumors (2016) [11] has made several changes in designated tumor entities, variants, and patterns.

Table 1 Framework for pathological classification of gliomas according to the 4th edition (2007) of the WHO classification of CNS tumors (modified from Komori [4])