How Brain Tumours Are Classified Today

A tumour name is more than a label: it records the basis on which a tumour has been classified. The Asian Oceanian Society of Neuropathology's ADAPTR recommendations explain how microscopic features and molecular information fit together for adult-type diffuse gliomas, and how classification can be described where diagnostic resources differ. Registry statistics answer a separate question: how often particular groups of tumours are recorded.

From the microscope to the molecule

The AOSNP-ADAPTR recommendations published in Brain Pathology in March 2026 describe a change in the fifth edition of the World Health Organization classification of central nervous system tumours, often shortened to WHO CNS5. For adult-type diffuse gliomas, this edition integrates molecular parameters with histological features in its diagnostic and grading criteria. Histology means examining tissue under a microscope; molecular information adds laboratory evidence about features of the tumour's biology.

The word integrated matters here. It describes bringing different kinds of evidence into a classification, rather than treating the appearance of tissue as the whole description. The recommendations state that molecular testing is crucial for most adult-type diffuse gliomas to fulfil WHO CNS5 diagnostic criteria. Their focus is this particular group, so the recommendations should not be read as a classification guide covering every brain tumour.

For readers of scientific literature, the distinction provides a useful starting point. A tumour label and the evidence used to establish that label belong together. When a paper describes an integrated diagnosis, the relevant question is what microscopic and molecular information the description includes. Keeping those terms clear helps readers understand the classification language without turning a general explanation into instructions for an individual diagnosis.

Diagnosis where resources differ

AOSNP stands for the Asian Oceanian Society of Neuropathology. Its ADAPTR initiative means Adapting Diagnostic Approaches for Practical Taxonomy in Resource-Restrained Regions. In the recommendations, the authors identify cost and technical barriers that can make molecular diagnostics infeasible in low-income and lower-middle-income countries. Their purpose is to adapt diagnostic approaches to available resources while following WHO guidance as closely as possible.

The recommendations distinguish five levels of diagnostic pathology services, labelled RL I through RL V. The authors identify RL I–IV as applicable to lower-middle-income countries. A resource level describes the diagnostic services available; it is separate from the name or grade assigned to a tumour. Reading the two kinds of label as if they meant the same thing would obscure the purpose of the framework.

At each resource level, ADAPTR recommends a histology-oriented integrated diagnosis format and provides diagnostic flow charts for adult-type diffuse gliomas. Its emphasis is on histopathological approaches with immunohistochemistry, a method that uses staining to reveal features in tissue. The molecular testing recommendations fall into three categories: "can be considered", "highly recommended" and "obligatory". These categories describe the framework's testing recommendations for reaching the next level of diagnosis.

The authors also distinguish the terminology used to report the result. Depending on the context, the format provides either a WHO CNS5 diagnosis with a CNS WHO grade, or an ADAPTR descriptive diagnosis with an ADAPTR histologic grade. Those names identify different reporting formats. They should remain visible when a classification is quoted, rather than being shortened to a grade with its accompanying framework omitted.

This makes the approach relevant to reading papers from settings with different laboratory resources. The resource level, the diagnostic format and the classification system give context to the tumour name. They help a reader see which kind of description a publication is using. The framework is an adaptation of WHO CNS5 for resource-restrained practice, as the authors describe it, rather than a statement that all settings have identical testing facilities.

What the numbers look like

The CBTRUS statistical report published in Neuro-Oncology in October 2025 describes primary brain and other central nervous system tumours diagnosed in the United States during 2018–2022. CBTRUS is the Central Brain Tumor Registry of the United States. Its figures are US registry data, including malignant and non-malignant tumours, and should not be presented as incidence figures for Asia.

For that US period, the report gives an average annual age-adjusted incidence of 26.05 per 100,000 people for all primary brain and other CNS tumours. The malignant category accounts for 6.86 per 100,000 and the non-malignant category for 19.19 per 100,000. The rates use the 2000 US standard population for age adjustment. A rate per 100,000 is a way to express incidence on a common population scale, rather than a percentage of tumours.

The report separately gives the share of all recorded tumours belonging to particular groups: gliomas account for 22.2%, glioblastoma for 13.7%, and meningioma for 42.6%, with the meningioma figure including malignant meningioma. These percentages describe the composition of the US dataset. They answer a different question from the population incidence rates and should retain their "of all tumours" denominator when quoted.

Among non-Hispanic Asian or Pacific Islander individuals in the US data, the reported incidence is 20.42 per 100,000 people. This demographic category is not an estimate for people living in Asia. For US children and adolescents aged 0–19 years, the report gives 5.99 per 100,000. Keeping the country, age group, period and units attached to each number makes the statistical comparison understandable.

Why classification shapes the literature

Classification and registry reporting serve different purposes, but both depend on clear descriptions. The ADAPTR recommendations explain how diagnoses and grades can be expressed under WHO CNS5 or an adapted format. The CBTRUS report shows why a statistical statement also needs a defined tumour group and population. A shared word such as glioma does not remove the need to read that surrounding detail.

For a paper about classification, look for the system named, the tumour group addressed and the diagnostic resources described. For a registry report, look for the geographical population, the years covered, the units and the denominator. These are reading questions about scientific terminology and statistics. The guide to neuro-oncology journals places this literature alongside the publications that carry it.