TUMOR TYPES: UNDERSTANDING BRAIN TUMORS

March 17, 2022

World Health Organization (WHO) Updates Official Classification of Tumors of the Central Nervous System

On May 9, 2016, the World Health Organization (WHO) published an official reclassification of Tumor Types of the Central Nervous System, which has moved the greater neuro-oncology field toward a more precise and accurate system of brain tumor classification. Based on information from expert neuropathologists and neuro-oncologists, the result of the updated WHO classifications, which integrate molecular information with histology, is that doctors will be better able to more accurately diagnose, make prognoses, plan treatment, and predict therapeutic response for patients. A more precise diagnosis and treatment plan is a win for patients.

Since the advent of new technology and capabilities for genomic sequencing, and in particular the seminal Cancer Genome Atlas project funded by the National Institutes of Health, recent molecular studies on brain tumors have begun to reveal the vast diversity of genetic and epigenetic alterations that exist between brain tumors. This biological heterogeneity often means tumors that may, at first blush, appear to be the same, may actually require a different approach to treatment – as well as the converse (i.e. tumors that may look different under the microscope may have common molecular alterations). Further studies have also shown that molecular signatures in tumor cells can define different groups of brain tumor types with distinctive characteristics, and that analyzing a tumor for mutations or deletions in certain genes or regions of chromosomes, can provide a deeper level of understanding of each tumor’s make-up.

Thus, it was critical that molecular data be integrated into traditional histopathology approaches to reclassify brain tumor types more effectively.

New integrated classifications will also improve future research and the development of new treatments by ensuring that patients participating in clinical trials are comparable within and across trials, and patients in clinical trials are correctly stratified based on their molecular signatures with targeted therapies most likely to benefit them. Additionally, the updated classifications will help provide more accurate analysis and understanding of experimental studies in the lab, as well as better interpretation of population-based disease trends that may help identify causes and risk factors. In short, this move away from traditional histopathology alone, to integrated classification with molecular characteristics, moves the brain tumor field further into the era of medicines that are highly targeted for a particular brain tumor patient.

You can access the reclassification document HERE.

There are more than 120 types of brain and central nervous system (CNS) tumors. Today, most medical institutions use the World Health Organization (WHO) classification system to identify brain tumors. The WHO classifies brain tumors by cell origin and how the cells behave, from the least aggressive (benign) to the most aggressive (malignant). Some tumor types are assigned a grade, ranging from Grade I (least malignant) to Grade IV (most malignant), which signifies the rate of growth. There are variations in grading systems, depending on the tumor type. The classification and grade of an individual tumor help predict its likely behavior. This section describes the most frequently diagnosed types.

Click on the links below for more information on specific tumor types.

The following tumor types are more common in children than in adults:

Keep in mind that many tumors have different subtypes; for example, an astrocytoma can be a juvenile pilocytic astrocytoma, an anaplastic astrocytoma or a glioblastoma. In addition, the same tumors sometimes have different names; even pathologists are not always consistent in what they call them. Finally, it is important to note that nonmalignant, or benign, brain tumors can be just as difficult to treat as malignant brain tumors.

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