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UK breast reports stage against the UICC's 8th edition, and the dataset warns against using the American AJCC 8th instead, because the two differ. The 9th edition, in force from January 2026, leaves breast staging alone; the one thing it changes is how a tumour is staged after chemotherapy given before surgery.
Three staging systems get quoted at a breast cancer patient and they are not interchangeable. The UICC TNM classification is the one UK reports use: the Royal College of Pathologists dataset in force names the eighth edition, reprints it as its appendix D, says it should be used for all tumours diagnosed after 1 January 2018, and warns in terms that 'it is recommended to use UICC TNM 8 (not AJCC TNM 8) as there are significant differences between the two staging systems'. The American Joint Committee on Cancer's eighth edition keeps the same anatomical categories but adds a prognostic stage that folds grade, oestrogen and progesterone receptor status, HER2 status and, for some hormone receptor-positive tumours, a genomic assay score into the stage group, which moves a large minority of patients up or down a stage; that system has its own page here (`ajcc-prognostic-stage-breast`) and UK clinicians do not usually quote it. NICE NG101 names no TNM edition and no AJCC prognostic stage anywhere in its recommendations, so a British treatment decision is not stranded by the difference.
The ninth edition of UICC TNM was published on 3 July 2025 and UICC recommends it take effect from 1 January 2026. For breast, in the committee's own words, 'the classification remains unchanged': the T, N and M categories and the stage groupings are the same as the eighth edition's. One thing was clarified, and it is the thing that matters most to anyone who has chemotherapy before surgery. The post-treatment y-pathological classification is now spelled out: ypT and ypN correspond to pT and pN, the ypT category 'must be based on the largest continuous focus of residual invasive cancer', not including treatment-related fibrosis, multiple residual foci are classified with the m suffix, and the report is recommended to add an estimate of the extent of residual disease by the residual cancer burden method (Brierley 2026). In other words, a 30 mm area of scar tissue with three 4 mm nests of cancer in it is ypT1a, not ypT2, and the residual cancer burden is what carries the rest of the information.
Two details of the eighth edition catch readers out and survive unchanged into the ninth. In situ disease is staged Tis with the type in brackets, Tis (DCIS), Tis (LCIS) or Tis (Paget's) for Paget disease of the nipple with no underlying carcinoma, so stage 0 on a letter means in situ disease. And T4d is not a size at all: it is inflammatory carcinoma, a clinical diagnosis, which is why an inflammatory breast cancer is stage III or IV from the day it is named however small the tumour turns out to be.
Most cancers start in the ducts and drain first to the axillary nodes, which is why the armpit is checked and a sentinel node is sampled.
Same organ: Triple-negative breast cancer (TNBC), HR-positive / HER2-negative breast cancer, HER2-positive breast cancer, Male breast cancer, Ductal carcinoma in situ (DCIS), High-risk early HR-positive breast cancer, HR-positive metastatic breast cancer after CDK4/6 inhibitors, HER2-low and HER2-ultralow metastatic breast cancer, Early HER2-positive breast cancer, HER2-positive breast cancer with brain metastases, Early triple-negative breast cancer, Metastatic triple-negative breast cancer, Basal-like 1 triple-negative breast cancer (BL1), Basal-like 2 triple-negative breast cancer (BL2), Mesenchymal triple-negative breast cancer (M), Mesenchymal stem-like triple-negative breast cancer (MSL), Luminal androgen receptor triple-negative breast cancer (LAR), Immunomodulatory triple-negative breast cancer (IM), Metaplastic breast carcinoma, Carcinoma with medullary pattern (medullary breast cancer), Adenoid cystic carcinoma of the breast, Apocrine carcinoma of the breast, Secretory carcinoma of the breast, BRCA-associated triple-negative breast cancer, Inflammatory breast cancer, Paget disease of the nipple, Phyllodes tumour of the breast, Invasive lobular carcinoma of the breast, Invasive breast carcinoma of no special type (invasive ductal carcinoma), Tubular carcinoma of the breast, Mucinous carcinoma of the breast, Papillary carcinomas of the breast (encapsulated, solid and invasive papillary), Invasive cribriform carcinoma of the breast, Invasive micropapillary carcinoma of the breast, Neuroendocrine neoplasms of the breast, Lobular carcinoma in situ (LCIS)
Showing the organ this term concerns: Breast cancer (all types).
Shares Tumour size on a breast report, and why it differs from the scan, Nottingham Prognostic Index (NPI), and PREDICT, Grade, stage and receptor status: three different things on one breast report, Ductal carcinoma in situ (DCIS).
Shares Tumour size on a breast report, and why it differs from the scan, Nottingham Prognostic Index (NPI), and PREDICT, Grade, stage and receptor status: three different things on one breast report, Ductal carcinoma in situ (DCIS).
Shares AJCC 8th edition prognostic stage for breast cancer, Grade, stage and receptor status: three different things on one breast report, Pathologic complete response (pCR), Breast cancer (all types).
Shares AJCC stage (TNM staging manual), Grade, stage and receptor status: three different things on one breast report, Stage, TNM staging.
Shares Lobular carcinoma in situ (LCIS), Carcinoma in situ (CIS), Ductal carcinoma in situ (DCIS), Breast cancer (all types).
Shares Residual cancer burden (RCB), Pathologic complete response (pCR), HER2-positive breast cancer, Breast cancer (all types).
Shares Grade, stage and receptor status: three different things on one breast report, Ductal carcinoma in situ (DCIS), Breast cancer (all types), Triple-negative breast cancer (TNBC).
Shares Tumour size on a breast report, and why it differs from the scan, Lobular carcinoma in situ (LCIS), Nottingham Prognostic Index (NPI), and PREDICT, Breast cancer (all types).