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who 2021 brain tumor classification ?

### The 2021 WHO Classification of Tumors of the Central Nervous System: A Leap Forward in Diagnostics

In 2021, the World Health Organization (WHO) released its fifth edition of the Classification of Tumors of the Central Nervous System (CNS). This publication, known colloquially as the “Blue Books,” provides a comprehensive and systematic approach to the classification of brain and spinal cord tumors—a critical tool for healthcare professionals worldwide involved in the diagnosis and treatment of these often complex conditions. As the sixth iteration of this internationally recognized standard, it places a particular emphasis on molecular diagnostics, reflecting significant advancements in the field since its last update in 2016.

#### A New Era for Classification

The 2021 edition builds on the work of the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (c-IMPACT-NOW), an organization that had been regularly publishing updates on CNS tumors, integrating the latest molecular research into the traditional histological classification system. The new approach reflects the understanding that brain tumor biology is far more complex than previously believed, necessitating a shift away from a purely histogenetic classification towards a more holistic molecular one.

One of the most significant changes in the 2021 classification is the classification of gliomas. These tumors, which arise from the glial cells in the brain and spinal cord, are now subdivided into adult-type diffuse gliomas, pediatric-type diffuse low-grade gliomas, pediatric-type diffuse high-grade gliomas, and circumscribed astrocytic gliomas. This shift underscores the importance of recognizing the distinct biological and clinical features of pediatric and adult gliomas—a critical distinction for tailoring treatment plans.

#### Molecular Markers: The Future of Diagnosis

The 2021 WHO classification places significant emphasis on molecular diagnostics, providing detailed guidelines for the use of molecular markers in tumor classification and grading. This was a logical progression from the 2016 edition, which first introduced molecular information into the diagnostic framework. The 2021 update refines these criteria further, particularly for diffuse gliomas, paving the way for a more precise and nuanced diagnosis.

This shift towards molecular diagnostics is particularly important because it can significantly impact patient outcomes. Accurate molecular profiling can guide clinicians in choosing the most effective treatment options. For example, methylome profiling, which involves the examination of DNA methylation patterns, may become a cornerstone of CNS tumor diagnostics. The precision offered by molecular markers can help differentiate between entities that are otherwise indistinguishable on a histological basis, making it a game-changer for the clinical management of brain tumors.

#### Simplification and Standardization

In addition to incorporating molecular markers, the 2021 WHO classification has also simplified and standardized the nomenclature, aligning it with other WHO blue books. This harmonization not only makes the new classification easier to use but also encourages better communication between pathologists and clinicians. The WHO Classification of Tumours Online further supports these goals by offering a synthesis of published evidence and practice, with a focus on linking diagnostic categories to management recommendations.

#### The Importance of Ongoing Research

While the 2021 classification represents a significant step forward, it is also a living document. The c-IMPACT-NOW consortium continues to publish updates based on emerging research, ensuring that the classification remains relevant and up-to-date. As new molecular targets are discovered and as our understanding of brain tumor biology deepens, the WHO Classification of Tumors of the CNS will continue to evolve, providing healthcare professionals with the tools they need to diagnose and treat these conditions effectively.

In conclusion, the 2021 WHO Classification of Tumors of the Central Nervous System marks a significant milestone in the field of neuro-oncology. By embracing molecular diagnostics and refining classification criteria, it sets the stage for improved patient outcomes and continues the ongoing journey towards personalized medicine in the treatment of brain tumors.

For anyone interested in diving deeper into the specifics of the 2021 WHO classification, including the 10 fundamental principles that guide this new system, I recommend the peer-reviewed articles and resources linked above, including the links to the official WHO article and the full text of the publication on PubMed. Additionally, you can explore the WHO Classification of Tumours Online for more detailed cytopathology reporting guidelines and diagnostic management recommendations.