World Health Organization classification of tumours of the breast 6th edition 2026

The 6th edition of the WHO Classification of Breast Tumours introduces both major and minor changes based on recent advances in our understanding of breast biology, developments in diagnostic modalities, identification of specific molecular targets and new treatment regimens necessitating modifications to pathology reporting and tumour biomarker categorisation. This review summarises the main changes that strive towards a classification of global relevance. In invasive carcinoma, predictive factors increasingly inform modern breast cancer treatment. The 6th edition provides an update on HER2 reporting categories following the DESTINY-Breast 04 and 06 trials. Terminologies used to classify invasive tumours are clarified, with the term 'variant' now reserved for molecular/genetic alterations. Invasive lobular carcinoma (ILC) with extracellular mucin is recognised as a new diagnostic entity with prognostic implications. The diagnosis of mucinous carcinoma (MC) is reserved for mucin secreting carcinomas with grade 1 or 2 morphology and a favourable biomarker profile. The diagnosis of malignant phyllodes tumours requires only four of the original five adverse histological criteria. Classification of neuroendocrine tumours (NETs) is revised, recognising that the unified model, promoted in the 5th edition, is difficult to apply to the breast. New approaches to the classification of adenomyoepithelioma are discussed but the 5th edition system is broadly retained. A new section on 'Small Diagnostic Samples' outlines the merits of non-operative biopsy diagnosis, the B coding system and the importance of multidisciplinary review. Changes to diagnostic practice and the emerging role of artificial intelligence, with advantages and challenges, are discussed in a new section on 'Digital Pathology'.

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Publication Details

Journal
Histopathology
Published
2026-04-21
DOI
https://doi.org/10.1111/his.70149
Primary Topic
Breast Lesions and Carcinomas
Type
article
Field-Weighted Citation Impact
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article

World Health Organization classification of tumours of the breast 6th edition 2026

Thomas H. Helbich, Stuart J. Schnitt, Shabnam Jaffer, E Adjei et al.
Histopathology
Breast Lesions and Carcinomas
article

World Health Organization classification of tumours of the breast 6th edition 2026

Thomas H. Helbich, Stuart J. Schnitt, Shabnam Jaffer, E Adjei, Roberto Salgado, Bharat Rekhi, Ayşegül A. Şahin, Sunil R. Lakhani, Katherine B. Geiersbach, C Sotiriou, Harshima Disvini Wijesinghe, Jennelle C. Hodge, Gary Man-Kit Tse, Edi Brogi, Blanca Iciar Indave Ruiz, Matteo Lambertini, Aleš Ryška, Andrew S Field, Stephen B. Fox, Joseph David Khoury, Anna Sapino, Kimberly H. Allison, Puay Hoon Tan, Christine Giesen, Cecily Quinn, Pavitratha Puspanathan, Ian Ellis, Dilani Lokuhetty, WCT Standing Editorial Board
article en

Abstract

The 6th edition of the WHO Classification of Breast Tumours introduces both major and minor changes based on recent advances in our understanding of breast biology, developments in diagnostic modalities, identification of specific molecular targets and new treatment regimens necessitating modifications to pathology reporting and tumour biomarker categorisation. This review summarises the main changes that strive towards a classification of global relevance. In invasive carcinoma, predictive factors increasingly inform modern breast cancer treatment. The 6th edition provides an update on HER2 reporting categories following the DESTINY-Breast 04 and 06 trials. Terminologies used to classify invasive tumours are clarified, with the term 'variant' now reserved for molecular/genetic alterations. Invasive lobular carcinoma (ILC) with extracellular mucin is recognised as a new diagnostic entity with prognostic implications. The diagnosis of mucinous carcinoma (MC) is reserved for mucin secreting carcinomas with grade 1 or 2 morphology and a favourable biomarker profile. The diagnosis of malignant phyllodes tumours requires only four of the original five adverse histological criteria. Classification of neuroendocrine tumours (NETs) is revised, recognising that the unified model, promoted in the 5th edition, is difficult to apply to the breast. New approaches to the classification of adenomyoepithelioma are discussed but the 5th edition system is broadly retained. A new section on 'Small Diagnostic Samples' outlines the merits of non-operative biopsy diagnosis, the B coding system and the importance of multidisciplinary review. Changes to diagnostic practice and the emerging role of artificial intelligence, with advantages and challenges, are discussed in a new section on 'Digital Pathology'.

Histopathology
Indiana University Health (US), The University of Sydney (AU), Beth Israel Deaconess Medical Center (US), Mayo Clinic (US), Nottingham University Hospitals NHS Trust (GB), Memorial Sloan Kettering Cancer Center (US), The University of Texas MD Anderson Cancer Center (US), Harvard University (US), Chinese University of Hong Kong (HK), Homi Bhabha National Institute (IN), Komfo Anokye Teaching Hospital (GH), Peter MacCallum Cancer Centre (AU), Lenox Hill Hospital (US), Institut Jules Bordet (BE), Vienna General Hospital (AT), Ente Ospedaliero Ospedali Galliera (IT), UNSW Sydney (AU), St Vincent's Hospital Sydney (AU), Antwerp University Hospital (BE), Indiana Cancer Consortium (US), Eye & Retina Surgeons (SG), St. Vincent's University Hospital (IE), Province of Antwerp (BE), University Hospital Hradec Králové (CZ), Ziekenhuisnetwerk Antwerpen Stuivenberg (BE), Sullivan Nicolaides Pathology (AU), Candiolo Cancer Institute (IT), Centre international de recherche sur le cancer (FR), Indiana University – Purdue University Indianapolis (US), University of Nebraska Medical Center (US), Medical University of Vienna (AT), University of Genoa (IT), The University of Notre Dame Australia (AU), Stanford University (US)
Good health and well-being
Openalex Percentile: Top 17%
Breast Lesions and Carcinomas
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