WHO Releases First-Ever Classification for Pediatric Tumors

By Marilynn Larkin

December 30, 2021

NEW YORK (Reuters Health) - The World Health Organization has produced its first classification of pediatric tumors, and it reflects the current transition away from mostly microscopy-driven systems of classification toward molecularly-driven classifications, the authors of a summary of the new edition say.

Previously, pediatric tumors were covered together with adult tumors in the respective organ system.

"Transitioning from the optical to the molecular era is obviously challenging, because it has always been the aim of the WHO to balance comparability with previous classifications and scientific progress," lead author Dr. Stefan Pfister of DKFZ Heidelberg, and principal author Dr. Rita Alaggio of IRCCS Ospedale Bambino Gesù in Rome, told Reuters Health in a joint email.

"To this end, for instance, the changes introduced in the brain tumor part of the classification were quite a paradigm shift and accompanied by quite some controversial discussions, since many of them are now primarily been diagnosed/defined based on their molecular features rather than their morphology, which has been the 'workhorse' for decades," they said.

"There are still areas that need further work," they noted, "as indicated in various places in the summary, e.g., in the area of pediatric high-grade gliomas, whose inter-tumoral heterogeneity is not yet satisfactorily captured."

"However," they added, "in most of the different areas of pediatric oncology, the integration of molecular features with morphology paves the way to a classification of tumors meant to not only serve as a categorization according to an up-to-date taxonomy, but also a central strategic tool in therapeutic decision making."

The review article by Drs. Pfister and Alaggio and colleagues, published in Cancer Discovery, summarizes the main features and updates of each chapter of the inaugural WHO Classification of Pediatric Tumors, which is organized by tumor site. Of note, the new pediatric "blue book" includes coverage of the hereditary cancer predisposition syndromes that are associated with about 10% of pediatric tumors, and identifies the challenges associated with diagnosis and treatment.

Mesenchymal tumors are still mostly classified by morphologic criteria in the new classification, with genetic analysis complementing the traditional approach; by contrast, central nervous system tumors and leukemias are mostly classified based on recurrent molecular or epigenetic alterations.

In coming updates, which WHO will make online between editions, this may soon be complemented by additional emerging technologies, such as more standardized proteomics and single-cell or liquid biopsy analyses.

Drs. Pfister and Alaggio said, "The classification is based on a multidisciplinary approach with contributions from scientists and clinicians involved in different areas of pediatric oncology, with the aim to provide an important tool not only for pathologists, but also for all disciplines of the medical team involved in the management of pediatric oncologic patients."

"It has always been the aspiration of the WHO to serve all parts of the world, independent of socio-economic status," they noted. "The pediatric classification is very much in line with this, because the diagnostic approach is always multi-layered, regardless of access to the latest technologies."

"Thus, a diagnosis purely based on morphology is still possible for each of the listed entities," they said. "But these are discouraged, if methods are available to increase diagnostic accuracy."

SOURCE: https://bit.ly/3FLBRWQ Cancer Discovery, online December 17, 2021.