The objective of the WHO Classification of Tumours (WHO Blue Books) is to provide a uniform nomenclature of human cancers that is accepted and used worldwide. A standardized classification is necessary for pathologists, clinical oncologists, and cancer registries. It forms a basis for collecting histologically and genetically stratified, population-based incidence rates and is a prerequisite for comparing cancer therapy trials conducted in different centres and countries.
The WHO Classification of Tumours (Blue Books) project was initiated by WHO through a resolution of the WHO Executive Board in 1956. The 1st edition was edited by WHO′s Dr Leslie Sobin and published by WHO in Geneva in 1967–1981. The 1st edition had a very simple format, presenting a list of accepted diagnostic terms together with the respective International Classification of Diseases for Oncology (ICD-O) morphology codes. The remainder of each volume comprised short descriptions of histological diagnostic criteria.
The 2nd edition, also edited by Dr Leslie Sobin, was published by Springer. It comprised 25 volumes published over the course of two decades (1982–2002). In the 2nd edition, descriptions of histological features were complemented by information about relevant immunohistochemical markers. Each tumour type was illustrated by at least one full-colour histological image.
IARC assumed responsibility for the WHO Blue Books project as of the 3rd edition, which comprised 10 volumes published over the course of 6 years (2000–2005). The series editors for the 3rd edition were Drs Paul Kleihues and Leslie Sobin. The launch of the 3rd edition marked a transformation in both content and layout. Each volume was richly illustrated with numerous histological images. Genetic diagnostic criteria were addressed in detail, and a wealth of epidemiological and clinical data was included.
The 4th edition was launched in 2006 under the guidance of series editors Drs Fred T. Bosman, Elaine S. Jaffe, Sunil R. Lakhani, and Hiroko Ohgaki and was completed in 2018. It comprises 12 volumes, plus two revised versions published in 2016 and 2017 (of the volumes “Tumours of the Central Nervous System” and “Tumours of Haematopoietic and Lymphoid Tissues”, respectively). The 4th edition served as a revision and an update of the 3rd, but it also highlighted the increasing importance of genetic information, with some tumours defined explicitly by specific genetic alterations.