Updating the grading criteria for adult diffuse gliomas: beyond the WHO2016CNS classification

• Published in: Brain tumor pathology Vol. 37; no. 1; pp. 1 - 4
• Main Author: Komori, Takashi
• Format: Journal Article
• Language: English
• Published: Singapore Springer Singapore 2020; Springer Nature B.V
• Subjects: Antibodies; Apoptosis; Biomarkers; Brain cancer; Cancer Research; Classification; Consortia; DNA methylation; Editorial; Glioma; Medical prognosis; Medicine; Medicine & Public Health; Mutation; Nervous system; Neurology; Neurosurgery; Oncology; Pathology; Tumors
• ISSN: 1433-7398; 1861-387X
• DOI: 10.1007/s10014-020-00358-y

[...]the WHO has never specified the actual cut-off number for differentiating grade II and III due to the non-reproducibility and inter-observer variability of the mitotic count, which may be caused by the following: discriminating mitoses, particularly granular ones, from apoptosis is often challenging; the specimen size varies; the diameter of the microscopic fields differs depending on the manufacturer; and the evaluation area may be different, whether evaluating 10 consecutive high-powered fields or an entire specimen. Since the discovery of IDH mutations, it has been suggested that the legacy grading scheme depending on the mitotic count may not be a strong predictor of the outcome of WHO grade II and III astrocytomas with IDH-mutant, although it is still considered valid for IDH-wildtype gliomas [12]. Standardization as well as optimization of the antigen retrieval protocol for Ki-67 across every institution is generally much more challenging than standardizing the mitotic counting approach. Interestingly enough, Shirahata et al. found that the overall survival of IDH-mutant diffuse astrocytic tumors was associated with the CDKN2A/B homozygous deletion status and the presence of necrosis; patients with CDKN2A/B homozygous deletion without necrosis, graded as WHO grade III anaplastic astrocytoma according to the current criteria, exhibited an equivalent survival rate to those with WHO grade IV glioblastoma, IDH-mutant with CDKN2A/B homozygous deletion and necrosis [13].