The definitive diagnosis and classification of individual cancers underpins the care of individual cancer patients, as well as research into cancer causation, prevention, diagnosis, and treatment. Traditionally, cancer classification has been based on consensus of histopathological opinion, with very limited consideration of molecular pathology. But new technologies are now transforming the field of pathology more rapidly than at any other time during the past 30 years, and it has become increasingly clear that the traditional approach to cancer classification is insufficient. Our understanding of cancer at a molecular level has now reached the point that this information must be included in diagnoses. Digital pathology and image analysis are also producing new insights, providing quantitative justification of many existing diagnostic criteria while challenging others. The rapid improvement in computer technology, including artificial intelligence, is already producing clinically applicable aids to diagnosis, and this trend is likely to accelerate.
There is an urgent need to integrate these facets of diagnosis into cancer classification internationally, and to update the WHO Classification of Tumours on a regular basis. IARC has been responsible for the WHO Classification of Tumours, also known as the WHO Blue Books, since the 3rd edition (2000–2005), which covered all organ sites in 10 volumes. The characteristics of each cancer type, including diagnostic criteria, pathological features, and associated molecular alterations, are described and illustrated in a strictly disease-oriented manner to provide the international standards for diagnosis and cancer research.