TNM staging system

Last revised by Daniel MacManus on 7 Jun 2024

The TNM staging system (officially known as the TNM classification system of malignant tumours) is a cancer staging system overseen and published by the Union for International Cancer Control (UICC). The American Joint Committee on Cancer (AJCC) publishes the AJCC Cancer Staging Manual which is based upon - and for the most part identical to - the TNM system.

The TNM system has been widely adopted for the cancers of many body systems as a replacement for idiosyncratic disease-specific classification systems.

TNM systematically describes the extent of malignancies - primarily on their anatomy - and categorises each malignancy by the status of the primary tumour (T), nodal involvement (N) and metastatic disease (M).

In general the TNM system is not used for paediatric cancers.

In 2021 the AJCC made changes to how it updates and releases Cancer Staging content 8. The AJCC shifted from a Cancer Staging Manual to a Cancer Staging System and moved away from Editions to Versions.

The next staging update, AJCC version 9 TNM staging, will be published electronically and will be released chapter by chapter. Updated Version 9 disease sites go into effect on January 1 following their release. All disease sites in the 8th Edition Cancer Staging Manual, published in October 2016 1,2, remain current until replaced with Version 9 7,8.

T, N, and M, are called categories, however the term stage is reserved for a grouping of TNM designations that have a similar prognosis.
Stages are numbered I through IV. Although often heard, it is incorrect to talk about the T or N or M stage of a tumour.

The precise details depend on the primary tumour site and/or histology but in general:

  • TX: primary tumour cannot be assessed

  • T0: no evidence of primary tumour

  • Tis: carcinoma in situ

  • T1: site/tumour specific, generally small

  • T2: site/tumour specific

  • T3: site/tumour specific, generally large

  • T4: site/tumour specific, generally direct extension into adjacent organs/tissues

  • NX: nodes cannot be assessed

  • N0: no regional nodal metastasis

  • N1: site/tumour specific

  • N2: site/tumour specific

  • N3: site/tumour specific

When tumours involve non-regional nodes, the M category is usually applied

  • M0: no distant metastasis

  • M1: distant metastasis present

NB: No MX category exists, it was removed in the 6th edition, if presence of metastases is not known the cancer is assigned M0 2

The TNM system has been expanded to include other measures:

  • R: resection status

  • V: vascular invasion

Additional prefixes can be appended to define the TNM stage:

  • c: clinical assessment data (e.g. cT1b)

  • p: pathological data

  • y: clinical (yc) or pathological (yp) data following systemic or radiation therapy be it prior to surgery or as a primary treatment

  • r: clinical or pathological staging at the time of retreatment or recurrence for disease progression

  • a: for cancers discovered at autopsy (e.g. aT1)

    • not for cancers known about or suspected prior to death

  • m: multiple primary tumours of the same histology in the same organ, e.g. T2(m) or T2(5), the latter meaning that there are five primary tumours

Whereas T, N, and M, are called categories, the stage refers to a grouping of TNM designations that have similar prognosis. Stages are numbered I through IV. In general, M1 disease indicates stage IV. Stage 0 is assigned to carcinoma in situ. Stages are further broken down into subgroups, indicated by capital letters A, B and C which follow after the stage number (e.g. Stage IIB). Subgrouping is defined for each cancer site and provides additional prognostic information.

The TNM idea, as we know it, was developed by the French surgeon Pierre Denoix and colleagues in the 1940s, culminating in a groundbreaking publication in 1952 3,4. Professor Denoix was Director of the Institut Gustave Roussy, the first health facility in Europe dedicated to cancer research and care.

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