The WHO Classification of Tumours (WCT) provides a definitive evidence-based classification of all cancer types to enable diagnosis and research worldwide, with the aim of improving patient care and cancer prevention.

The 5th edition of the WHO Classification of Tumours introduces a formal hierarchical classification based on Linnaean principles, and it recognises the multidisciplinary nature of cancer diagnosis and classification. For the first time, the 5th edition uses a relational database to facilitate the organisation and publication of the contents of the WHO Blue Books online at - https://tumourclassification.iarc.who.int. This approach positions the classification for regular revisions to keep pace with scientific advances. It also aligns with planned revisions of the classification on a 5-year rolling basis and allows an evidence-based approach. Another new aspect of the 5th edition series is that it is now guided by an Editorial Board. Two consensus meetings are held for each book, the first to prepare the classification and authorship and the second to review and finalize the material.

The editorial board consists of a Chair, the Head of the WHO Classification of Tumours, Standing members, who serve three-year terms, and Expert members, who serve for the duration required to develop and publish the Blue Book for which they are appointed. Editors, whether standing or expert members, have equal status in setting the classification.

Standing members are nominated by major pathology and other diagnostic specialty organisations around the world. They are chosen to represent as wide a range of expertise and geography as possible. At any one time there may be up to 16 standing members. They serve three-year terms, and then rotate off the editorial board. To ensure continuity and knowledge transfer, they may be reappointed for a second term of one to a maximum of three additional years.

Expert members are chosen in consultation with Standing members of the board on the basis of bibliometric searches, and knowledge of the field. On occasion, we may ask external bodies for their nominations. Expert members include pathologists, oncologists, surgeons, radiologists, molecular biologists, or other cancer specialists to ensure multidisciplinary input. Decisions on membership take into account our diversity requirements. Expert editors may serve for up to two editions.

Members of the editorial board produce a draft classification based on the previous one, which is then discussed and refined at the first editorial board consensus meeting.

The result is a working draft classification, which is then entered into the Blue Book online submission system (BBOSS), a database that permits considerable flexibility in the placement and organisation of entries while they are being written and thereafter, until proofs are produced.

Authors are asked to write their sections in three to four months and submit their drafts a month before the second Expert editorial board meeting. Sections are succinct and follow a strict organisational framework.

The second Expert editorial board meeting occurs 5 months after the first and is a review of the submitted content. During this meeting, changes may be made to the classification, the submitted text, and the figures. Discussions take account of the potential impact of changes for patients, and for limited resource settings. Missing information is identified and any gaps are filled during the month after the meeting. Following this the volume is checked by the in-house pathology team, with assistance from the editors and authors of each section. The book then moves to technical editing and finally proofs before publication on the website and in print. The entire process takes 12 - 14 months for most volumes, depending on the amount of work involved.

Authors are selected using the same methods used for Expert editors, with increasing reliance on bibliometric searches using an in-house software developed for the purpose. The emphasis is on authors who have substantive publications in the field during the previous five years, taking into account geography and expertise. It is not unusual to invite authors from various specialities such as oncology, surgery, genetics, or radiology, to provide multidisciplinary input where needed.

Yes, we have close links with other international organisations that use the classification or produce information that may influence the classification. This includes organisations involved in genetics, pathology, radiology and staging. On occasion we work with international organisations that specialise in specific areas, for instance the IASLC, and the c-IMPACT group.

The WHO Classification of Tumours provides an international consensus on the characteristics of tumours which underpin their diagnosis. However, IARC does not recommend changes to practice, regulations, legislation, or public health interventions, which remain the responsibility of individual governments and other international organizations. It does not endorse any commercial products, approval of which is the responsibility of individual governments and healthcare agencies.

The program at IARC is funded exclusively from sales of the WHO Blue Books and/or subscription to the website. We keep the costs as low as possible and operate on a not-for-profit basis. We also subsidise the books and the website for individuals from low- and middle-income countries.

The Tumour Classification Online (https://tumourclassification.iarc.who.int) content is essentially the same, with links to the evidence cited within the text on the website. Importantly, the website offers an ever-growing library of whole-slide images of representative cases.

The team running the classification is based at the International Agency for Research on Cancer (IARC), in Lyon, France. IARC also acts as the publisher for the classification and hosts the subscription website. The WHO Blue Books are distributed by WHO Press in Geneva (bookorders@who.int).

We have published the methodology used by the WHO Classification of Tumours in multiple scientific articles, including:

The 2021 WHO Classification of Tumors of the Central Nervous System: a summary. Louis DN, Perry A, Wesseling P, Brat DJ, Cree IA, Figarella-Branger D, Hawkins C, Ng HK, Pfister SM, Reifenberger G, Soffietti R, von Deimling A, Ellison DW. Neuro Oncol. 2021 Jun 29:noab106. doi: 10.1093/neuonc/noab106. Online ahead of print. PMID: 34185076

Cree IA, Tan PH, Travis WD, Wesseling P, Yagi Y, White VA, Lokuhetty D, Scolyer RA.Counting mitoses: SI(ze) matters! Mod Pathol. 2021 Jun 2. doi: 10.1038/s41379-021-00825-7. Online ahead of print.PMID: 34079071.

Leske H, Dalgleish R, Lazar AJ, Reifenberger G, Cree IA. A common classification framework for histone sequence alterations in tumours: an expert consensus proposal. J Pathol. 2021 Jun;254(2):109-120. doi: 10.1002/path.5666. Epub 2021 May 7. PMID: 33779999

Chow ZL, Indave BI, Lokuhetty MDS, Ochiai A, Cree IA, White VA. Misleading terminology in pathology: lack of definitions hampers communication. Virchows Arch. 2021 Apr 2. doi: 10.1007/s00428-021-03069-7. Online ahead of print. PMID: 33796909

Washington MK, Goldberg RM, Chang GJ, Limburg P, Lam AK, Salto-Tellez M, Arends MJ, Nagtegaal ID, Klimstra DS, Rugge M, Schirmacher P, Lazar AJ, Odze RD, Carneiro F, Fukayama M, Cree IA; WHO Classification of Tumours Editorial Board. Diagnosis of digestive system tumours. Int J Cancer. 2021 Mar 1;148(5):1040-1050. doi: 10.1002/ijc.33210. Epub 2020 Nov 19. PMID: 32674220

Cree IA, Indave Ruiz BI, Zavadil J, McKay J, Olivier M, Kozlakidis Z, Lazar AJ, Hyde C, Holdenrieder S, Hastings R, Rajpoot N, de la Fouchardiere A, Rous B, Zenklusen JC, Normanno N, Schilsky RL; IC3R participants.The International Collaboration for Cancer Classification and Research. Int J Cancer. 2021 Feb 1;148(3):560-571. doi: 10.1002/ijc.33260. Epub 2020 Oct 9. PMID: 32818326

Tan PH, Ellis I, Allison K, Brogi E, Fox SB, Lakhani S, Lazar AJ, Morris EA, Sahin A, Salgado R, Sapino A, Sasano H, Schnitt S, Sotiriou C, van Diest P, White VA, Lokuhetty D, Cree IA; WHO Classification of Tumours Editorial Board. The 2019 World Health Organization classification of tumours of the breast. Histopathology. 2020 Aug;77(2):181-185. doi: 10.1111/his.14091. Epub 2020 Jul 29. PMID: 32056259

Quezada-Marín JI, Lam AK, Ochiai A, Odze RD, Washington KM, Fukayama M, Rugge M, Klimstra DS, Nagtegaal ID, Tan PH, Arends MJ, Goldblum JR, Cree IA, Salto-Tellez M. Gastrointestinal tissue-based molecular biomarkers: a practical categorisation based on the 2019 World Health Organization classification of epithelial digestive tumours. Histopathology. 2020 Sep;77(3):340-350. doi: 10.1111/his.14120. Epub 2020 Jul 4. PMID: 32320495 Review.

Louis DN, Wesseling P, Aldape K, Brat DJ, Capper D, Cree IA, Eberhart C, Figarella-Branger D, Fouladi M, Fuller GN, Giannini C, Haberler C, Hawkins C, Komori T, Kros JM, Ng HK, Orr BA, Park SH, Paulus W, Perry A, Pietsch T, Reifenberger G, Rosenblum M, Rous B, Sahm F, Sarkar C, Solomon DA, Tabori U, van den Bent MJ, von Deimling A, Weller M, White VA, Ellison DW. cIMPACT-NOW update 6: new entity and diagnostic principle recommendations of the cIMPACT-Utrecht meeting on future CNS tumor classification and grading. Brain Pathol. 2020 Jul;30(4):844-856. doi: 10.1111/bpa.12832. Epub 2020 Apr 19. PMID: 32307792

Uttley L, Indave BI, Hyde C, White V, Lokuhetty D, Cree I.Invited commentary-WHO Classification of Tumours: How should tumors be classified? Expert consensus, systematic reviews or both? Int J Cancer. 2020 Jun 15;146(12):3516-3521. doi: 10.1002/ijc.32975. Epub 2020 Apr 2. PMID: 32170735 Free PMC article.

Elder DE, Bastian BC, Cree IA, Massi D, Scolyer RA. The 2018 World Health Organization Classification of Cutaneous, Mucosal, and Uveal Melanoma: Detailed Analysis of 9 Distinct Subtypes Defined by Their Evolutionary Pathway. Arch Pathol Lab Med. 2020 Apr;144(4):500-522. doi: 10.5858/arpa.2019-0561-RA. Epub 2020 Feb 14. PMID: 32057276 Free article. Review.

Cree IA, Indave BI. Commentary: Cancer research quality and tumour classification. Tumour Biol. 2020 Feb;42(2):1010428320907544. doi: 10.1177/1010428320907544. PMID: 32098581

Cree IA, White VA, Indave BI, Lokuhetty D. Revising the WHO classification: female genital tract tumours. Histopathology. 2020 Jan;76(1):151-156. doi: 10.1111/his.13977. PMID: 31846528.

Nagtegaal ID, Odze RD, Klimstra D, Paradis V, Rugge M, Schirmacher P, Washington KM, Carneiro F, Cree IA; WHO Classification of Tumours Editorial Board.The 2019 WHO classification of tumours of the digestive system. Histopathology. 2020 Jan;76(2):182-188. doi: 10.1111/his.13975. Epub 2019 Nov 13. PMID: 31433515 Free PMC article.

Nicholson AG, Sauter JL, Nowak AK, Kindler HL, Gill RR, Remy-Jardin M, Armato SG 3rd, Fernandez-Cuesta L, Bueno R, Alcala N, Foll M, Pass H, Attanoos R, Baas P, Beasley MB, Brcic L, Butnor KJ, Chirieac LR, Churg A, Courtiol P, Dacic S, De Perrot M, Frauenfelder T, Gibbs A, Hirsch FR, Hiroshima K, Husain A, Klebe S, Lantuejoul S, Moreira A, Opitz I, Perol M, Roden A, Roggli V, Scherpereel A, Tirode F, Tazelaar H, Travis WD, Tsao MS, van Schil P, Vignaud JM, Weynand B, Lang-Lazdunski L, Cree I, Rusch VW, Girard N, Galateau-Salle F. EURACAN/IASLC Proposals for Updating the Histologic Classification of Pleural Mesothelioma: Towards a More Multidisciplinary Approach. J Thorac Oncol. 2020 Jan;15(1):29-49. doi: 10.1016/j.jtho.2019.08.2506. Epub 2019 Sep 20. PMID: 31546041 Free article.

Salto-Tellez M, Cree IA.Cancer taxonomy: pathology beyond pathology. Eur J Cancer. 2019 Jul;115:57-60. doi: 10.1016/j.ejca.2019.03.026. Epub 2019 May 17. PMID: 31108243

Rindi G, Klimstra DS, Abedi-Ardekani B, Asa SL, Bosman FT, Brambilla E, Busam KJ, de Krijger RR, Dietel M, El-Naggar AK, Fernandez-Cuesta L, Klöppel G, McCluggage WG, Moch H, Ohgaki H, Rakha EA, Reed NS, Rous BA, Sasano H, Scarpa A, Scoazec JY, Travis WD, Tallini G, Trouillas J, van Krieken JH, Cree IA. A common classification framework for neuroendocrine neoplasms: an International Agency for Research on Cancer (IARC) and World Health Organization (WHO) expert consensus proposal. Mod Pathol. 2018 Dec;31(12):1770-1786. doi: 10.1038/s41379-018-0110-y. Epub 2018 Aug 23. PMID: 30140036