ASCO 2017: Tackling the WHO Classification of Central Nervous System Tumors

Analyzing and managing brain tumors despite limitations

Naveed Saleh, MD, MS

Disclosures

August 17, 2017

During the past 50 years, the World Health Organization (WHO) has sponsored several tumor classifications that were developed by international experts and which cover head and neck tumors, endocrine tumors, breast tumors, and many other tumor types.[1] These classifications are used globally for diagnosis and treatment. [2] For brain tumors, findings are compiled into the WHO Classification of Tumours of the Central Nervous System,[3] billed as an "authoritative, concise reference book" that "provides an international standard for oncologists and pathologists."

The problem with the WHO classification, however, is that it is not definitive. With insights into the molecular basis of human tumors being elucidated at a dizzying rate, the diagnosis and management of brain tumors continuously evolve. The WHO classification, which is updated periodically, is by nature a work in progress that becomes more dated with each passing day.

At a June 3, 2017, session at the annual meeting of the American Society of Clinical Oncology (ASCO),[4] presenters tackled the issue of analyzing and managing brain tumors—in particular, pediatric brain tumors—in light of limitations of the official WHO classification system. According to lecturer Mark W. Kieran, MD, PhD, a pediatric hematologist-oncologist and director of pediatric neuro-oncology at Dana-Farber/Boston Children's Cancer and Blood Disorders Center, "The point of presenting at a meeting like ASCO, with people coming from all over the world, is that it's an opportunity to let people know the strengths and weaknesses of the current classification schemes so that they can deal with it accordingly. That will give us time to evaluate additional advances and eventually make the edits that are needed in the WHO [classification]."

Issues With the WHO Classification

This new edition of the WHO Classification of Tumours of the Central Nervous System is merely a revised version and not "brand-new." In fact, the last time WHO experts met to formally issue a new edition was before the publication of the 2007 one (WHO 2007). The 2016 revised edition was based on a 3-day meeting that, according to Dr Kieran, was weighted with experts whose focus was adult neuropathology. Ultimately, the limited number of pediatric experts and brief duration of the meeting influenced the classification system, with pediatric brain tumors most affected.

The issue with pathology in the past is that it has predominantly been based on the microscopic appearance of the cell. The microscope is 500-year-old technology.

Co-lecturer Christine Fuller, MD, neuropathologist and professor of pathology at Cincinnati Children's Hospital Medical Center, noted that the WHO cycles through different types of cancer. The new edition of the WHO classification for central nervous system tumors was apparently not scheduled for revision quite yet. "The brain tumor community made such a ruckus because there has been so much data and so many molecular discoveries that have come out since the WHO 2007 that there was insistence that the WHO allow for the release of something now," explained Dr Fuller. "[The WHO classification] was very outdated. There was a smattering of molecular [characterization] that was in there, but there are new technologies that have come up since that time. We didn't have methylation profiling back then. We didn't have deep-sequencing and whole exome sequencing, or at least it wasn't nearly as available [or affordable]."

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