Practical procedures for the integrated diagnosis of astrocytic and oligodendroglial tumors

The publication of the 2016 World Health Organization Classification of Tumors of the Central Nervous System (2016 WHO CNS) represented a major change in the classification of brain tumors. However, many pathologists in Japan cannot diagnose astrocytic or oligodendroglial tumors according to the 2016 WHO CNS due to financial or technical problems. Therefore, the Japan Society of Brain Tumor Pathology established a committee for molecular diagnosis to facilitate the integrated diagnosis of astrocytic and oligodendroglial tumors in Japan. We created three levels of diagnoses: Level 1 was defined as simple histopathological diagnosis using hematoxylin and eosin staining and routine cell lineage-based immunostaining. Level 2 was defined as immunohistochemical diagnosis using immunohistochemical examinations using R132H mutation-specific IDH1, ATRX, and/or p53 antibodies. Level 3 was defined as molecular diagnosis, such as diagnosis based on 1p/19q status or the mutation status of the IDH1 and IDH2 genes. In principle, astrocytic and oligodendroglial tumors should be diagnosed based on the 2016 WHO CNS and/or cIMPACT-NOW criteria; however, the findings obtained through our diagnostic flowchart can be added to the histological diagnosis in parentheses. This classification system would be helpful for pathologists with limited resources.