There is a high medical need to improve treatment outcome for high-grade and low-grade glioma since no curative treatment is available. To achieve this goal, a broader understanding is needed of the causes of inter-and intratumoral heterogeneity; glioma dedifferentiation and invasion; the major determinants of malignancy and treatment failure in glioma patients. Patient-derived organoid (PDOs) of high-grade gliomas and low-grade gliomas will be used to identify the mechanisms that underlie this malignant behaviour and treatment resistance. This insight may be used to develop patient avatars to simultaneously test multiple new treatment modalities that are predictive for survival and quality of life of glioma patients.