Résumé
Glial tumors are known to be difficult to classifify. Due to insights in genetic alterations of gliomas the 2016 WHO classification of tumors in CNS presents a new diagnostic approach introducing integrated histological and molecular diagnosis in the classification of diffuse gliomas. This approach will probably lead to better reproducibility between pathologists than histopathological criteria alone. However, the classification still defines histological grades of malignancy, and histologic grade is still an important factor in deciding treatment. For diffuse infiltrating gliomas the grades are GII (LGG), GIII and GIV (HGG). GII gliomas, despite their low grade, are infiltrative and will progress to higher grades of malignancy. The duration of transition from GII to GIII is highly variable. Identification of predictive markers of malignant progression could help identify patients who could benefit from early adjuvant treatments. We have studied the heterogeneity within GII gliomas, and find that some tumors harbor foci with histopathological and molecular features similar to higher grade. We suggest that these foci may represent initiation of malignant transformation. The term GII+ could be applied to these tumors indicating an intermediate grade, and the identification of these tumors can be valuable in order to optimize individual treatment.