Every new classification depends on its prognostic power and on the type of treatment given. With the rapid evolution of diagnostic methods and the advance in new treatments, there is much less reliable information available on how patients with newly defined brain tumour entities should be treated and what to expect from the current treatments.

The goal is to determine whether the new 2021 WHO classification, based on cIMPACT-NOW recommendations, results in more homogeneous patient groups than the old 2016 classification. Furthermore, it will help derive provisional guidelines on how patients with these newly defined tumour entities are best treated. These recommendations will be based on the experience of EORTC investigators with chosen treatments and their experience as reported in this data collection report.

• Age ≥ legal age of consent
• Newly diagnosed or recurrent primary brain tumours within one of the 17 cohorts of interest
• Archival tumour tissue from primary tumour available at the site. Representative tissue from first surgery is preferred, but tissue from surgery for recurrence is allowed. Exception: only tissue from first surgery is allowed for Cohort 16.
• Available MRI/CT scans from primary brain tumour at initial diagnosis
• Patient's consent

Deceased patient:

The clinical data and/or biological material and/or CT/MRI/PET images can be accessed and used if at least one of the following three conditions is met:

• The patient agreed beforehand in his/her lifetime to a further use of his/her data and/or biological material and/or CT/MRI/PET images, or,
• There is consent of a relative to use data and/or biological material and/or CT/MRI/PET images of the deceased patient, or,
• There is a reference to a corresponding legal declaration covering the exemption in case of the impossibility or disproportion of getting access to an informed consent (e.g., causing strain on relatives of deceased patients).

Additionally, in all cases the following three points need to be fulfilled:

• No documentation of previous objection of the patient to the (re-)use of their data, biological material, CT/MR/PET images for research purposes
• A notification to an ethics committee for the re-use of these data, biological material and CT/MRI/PET images
• Any other national requirements are fulfilled, if applicable

Adult patients with newly diagnosed or recurrent primary brain tumours, notably those considered to be very rare brain tumours or rare subtypes of common brain tumours will be included. Patients diagnosed between 2011 and 2025.