{"entity":{"id":"who-breast-classification","kind":"term","name":"The WHO classification of breast tumours, and what the 6th edition changed","aka":["WHO classification of tumours of the breast","WHO breast classification","WHO 5th edition breast","WHO 6th edition breast","blue book","WHO blue book breast","breast tumour classification","special type","no special type","NST"],"tldr":"The book that decides what a breast tumour is called. Its fifth edition (2019) is the one UK reports are written against in 2026; its sixth edition was set out in April 2026, in the editorial board's own summary of it, and changed the vocabulary, the HER2 reporting categories and the rules for several rare types.","summary":"The WHO Classification of Tumours of the Breast is the reference every pathology report, guideline and trial protocol implicitly cites when it names a tumour. The fifth edition (2019, summarised for pathologists by Tan 2020) is the edition the UK reporting dataset in force is written against: it keeps invasive breast carcinoma of no special type as the large default group, into which it folded the former medullary, oncocytic, lipid-rich, glycogen-rich, sebaceous and pleomorphic carcinomas as patterns rather than types, and it keeps the special types, lobular, tubular, mucinous, cribriform, papillary, secretory, adenoid cystic, apocrine, micropapillary, metaplastic and neuroendocrine, as separate entities. Nearly every breast page here is written to that edition.\n\nThe sixth edition was published in April 2026 (Quinn 2026). Five of its changes matter to a reader holding a report. It fixes the vocabulary: a subtype differs clinically, histologically or genetically in a way that changes treatment or outcome, a pattern differs only in appearance, and the word variant is discouraged for anything but a molecular or genetic alteration, so a report or a website using variant to mean an unusual appearance is using the older, looser sense. It updates the HER2 reporting categories after the DESTINY-Breast04 and DESTINY-Breast06 trials, so that cases with no membrane staining at all are distinguished from cases with any membrane staining, because that boundary now decides who is offered trastuzumab deruxtecan. It recognises invasive lobular carcinoma with extracellular mucin as an emerging subtype that behaves more aggressively than classical lobular cancer. It moves mucinous carcinomas that are high grade, oestrogen receptor negative or HER2 positive out of mucinous carcinoma and into carcinoma of no special type with mucin production. It abandons the unified neuroendocrine neoplasm model the fifth edition applied across organs, on the ground that it is difficult to apply to the breast, and stops recommending routine neuroendocrine staining of ordinary carcinoma. And it lowers the bar for malignant phyllodes tumour from all five adverse histological features to four of the five.\n\nNone of that has reached a British report yet. The Royal College of Pathologists dataset in force (G148, version 3, November 2024) states that its histological subtypes were updated in line with the fifth edition, and it is due for full review in November 2026. So in 2026 a UK report is a fifth-edition report, and the sixth edition is what the next one will be written against.","asOf":"2026-09-25","wikipedia":"https://en.wikipedia.org/wiki/WHO_Blue_Books","links":[{"label":"Quinn et al., Histopathology 2026;89(2):199 to 218: World Health Organization classification of tumours of the breast, 6th edition 2026","url":"https://doi.org/10.1111/his.70149"},{"label":"Tan et al., Histopathology 2020: the 2019 WHO classification of tumours of the breast (5th edition)","url":"https://doi.org/10.1111/his.14091"},{"label":"Royal College of Pathologists G148: dataset for histopathological reporting of breast disease in surgical excision specimens of breast cancer, version 3, November 2024 (full review due November 2026)","url":"https://www.rcpath.org/resourceLibrary/g148-dataset-for-histopathological-reporting-of-breast-disease-in-surgical-excision-specimens-of-breast-cancer.html"}],"tags":[],"related":["histology","tumour-differentiation","her2-low","basal-like"],"cancers":["breast-cancer","invasive-breast-carcinoma-no-special-type","invasive-lobular-carcinoma","mucinous-carcinoma-breast","phyllodes-tumour","neuroendocrine-neoplasms-breast","medullary-pattern-breast-carcinoma"],"sections":["diagnostics"],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["terminal-duct-lobular-unit","nottingham-grade","her2-testing-uk-breast","her2-low"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":["Why the corpus still cites the fifth edition. The pages in this family were written against the edition the pathologist follows, not the newest one published. Where the sixth edition changes a name or a rule, this term records the change and the page it affects keeps the fifth-edition wording until the UK dataset moves, so that the page and the report in the reader's hand agree."],"category":"Pathology"},"route":"/terms/who-breast-classification/","neighbours":{"term":[{"id":"basal-like","kind":"term","name":"Basal-like breast cancer","route":"/terms/basal-like/"},{"id":"terminal-duct-lobular-unit","kind":"term","name":"Ducts, lobules and the terminal duct lobular unit","route":"/terms/terminal-duct-lobular-unit/"},{"id":"her2-testing-uk-breast","kind":"term","name":"HER2 testing in the UK: reflex ISH, the ratio against the copy number, and where the UK differs from ASCO/CAP","route":"/terms/her2-testing-uk-breast/"},{"id":"her2-low","kind":"term","name":"HER2-low and HER2-ultralow","route":"/terms/her2-low/"},{"id":"histology","kind":"term","name":"Histology","route":"/terms/histology/"},{"id":"nottingham-grade","kind":"term","name":"Nottingham grade (breast cancer grade 1, 2 and 3)","route":"/terms/nottingham-grade/"},{"id":"tumour-differentiation","kind":"term","name":"Tumour differentiation (well / moderately / poorly differentiated)","route":"/terms/tumour-differentiation/"}],"cancer":[{"id":"breast-cancer","kind":"cancer","name":"Breast cancer (all types)","route":"/cancers/breast-cancer/"},{"id":"medullary-pattern-breast-carcinoma","kind":"cancer","name":"Carcinoma with medullary pattern (medullary breast cancer)","route":"/cancers/medullary-pattern-breast-carcinoma/"},{"id":"breast-her2-positive","kind":"cancer","name":"HER2-positive breast cancer","route":"/cancers/breast-her2-positive/"},{"id":"breast-hr-positive","kind":"cancer","name":"HR-positive / HER2-negative breast cancer","route":"/cancers/breast-hr-positive/"},{"id":"invasive-breast-carcinoma-no-special-type","kind":"cancer","name":"Invasive breast carcinoma of no special type (invasive ductal carcinoma)","route":"/cancers/invasive-breast-carcinoma-no-special-type/"},{"id":"invasive-lobular-carcinoma","kind":"cancer","name":"Invasive lobular carcinoma of the breast","route":"/cancers/invasive-lobular-carcinoma/"},{"id":"lobular-carcinoma-in-situ","kind":"cancer","name":"Lobular carcinoma in situ (LCIS)","route":"/cancers/lobular-carcinoma-in-situ/"},{"id":"mucinous-carcinoma-breast","kind":"cancer","name":"Mucinous carcinoma of the breast","route":"/cancers/mucinous-carcinoma-breast/"},{"id":"neuroendocrine-neoplasms-breast","kind":"cancer","name":"Neuroendocrine neoplasms of the breast","route":"/cancers/neuroendocrine-neoplasms-breast/"},{"id":"phyllodes-tumour","kind":"cancer","name":"Phyllodes tumour of the breast","route":"/cancers/phyllodes-tumour/"},{"id":"tnbc","kind":"cancer","name":"Triple-negative breast cancer (TNBC)","route":"/cancers/tnbc/"}],"section":[{"id":"diagnostics","kind":"section","name":"Diagnostics & Biomarkers","route":"/fronts/diagnostics/"}]}}