WHO Launches a New Classification System for Pediatric Tumors, Incorporating Morphology, Immunohistochemistry Analysis, and Molecular Characteristics

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A review article by Pfister et al published in Cancer Discovery summarizes the inaugural classification of pediatric tumors soon to be published by the International Agency for Research on Cancer as part of the new World Health Organization (WHO) Classification of Tumors series, including an online version. The resource reflects the rapid transition from a mostly microscopy-driven classification to a molecularly based system and takes into account recent discoveries in pediatric tumor genomics.

Although, worldwide, cancer is a relatively rare disease in children and adolescents—each year about 400,000 children and adolescents are diagnosed with cancer—it is the leading cause of death in this young population. Research shows that childhood tumors are fundamentally different from those occurring in adults. Commonly diagnosed cancers in children and adolescents include leukemias, lymphomas, central nervous system tumors, sarcomas of bone and soft tissue, neuroblastoma, retinoblastoma, rhabdoid tumors, liver tumors, renal tumors, germ cell tumors, and other rare cancers.

Although pediatric and adult cancer tumors histologically appear to be of the same type, pediatric tumors often have distinctive etiology and pathogenesis. The WHO Classification of Pediatric Tumors, published as part of its fifth edition of the Classification of Tumors series, is organized according to organ sites and provides a single, state-of-the-art compendium of pediatric tumor types.

Clinical Significance

This new edition of the WHO Classification of Pediatric Tumors provides a basis for a multilayered diagnostic process that reflects two important aspects of care: meeting the needs of regions with varying level of access to state-of-the-art molecular technologies; and acknowledging the current transition from a traditional system of classification that is focused on cell type to an integrated approach that comprises many newly recognized molecular entities.


  • Pediatric cancer tumors are fundamentally different from adult tumors in terms of tumor types, etiology, biology, and therapeutic approaches.
  • The WHO Classification of Pediatric Tumors, the first classification of pediatric cancers that may be diagnosed in childhood or adolescence, follows a hierarchic classification and lists tumors by site, category, family, and type.
  • The classification reflects the general transition from traditional diagnostic approaches based on histologic/microscopic findings and immunohistochemistry to the new technologies for molecular diagnosis based on tumor genomics.

“It is difficult to predict whether molecular platform analyses or even liquid biopsies will fully replace histologic diagnosis on tumor tissue biopsies in the future. However, it is increasingly clear that molecular techniques are providing a new, powerful lens to current histologic evaluation, while it will remain of key importance to actually investigate representative tumor material,” concluded the study authors.

“Pediatric tumors differ radically from adult tumors in terms of tumor types, etiology, biology, and therapeutic approaches,” said first author Stefan M. Pfister, MD, Director of the Hopp Children’s Cancer Center Heidelberg in Germany. “Therefore, a pediatric age-focused classification is an instrumental step in allowing practitioners to identify the best treatment option on the basis of the most precise and accurate diagnosis.”

Dr. Pfister, of Hopp Children’s Cancer Center Heidelberg, is the corresponding author of this study.

Disclosure: The study was funded by the German Childhood Cancer Foundation, the German Federal Ministry of Education and Research, the Everest Centre for Research Into Low-grade Paediatric Brain Tumours (The Brain Tumour Charity), the Pediatric Low-Grade Astrocytoma Fund at the Pediatric Brain Tumor Foundation, the German Research Foundation (Deutsche Forschungsgemeinschaft), the Marjorie K. Harmer Endowment for Research in Pediatric Pathology, University of Pittsburgh School of Medicine, the National Institutes of Health, Children with Cancer UK, Great Ormond Street Hospital Children’s Charity, Olivia Hodson Cancer Fund, Cancer Research UK, and the UK National Institute of Health Research. For full disclosures of the study authors, visit

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.