TNM staging system

Last revised by Daniel J Bell on 8 Dec 2022

The TNM staging system (officially known as the TNM classification system of malignant tumors) 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. It is currently in its eighth edition, published in October 2016 1,2. The ninth edition is scheduled for publication in 2024 6.

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

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

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 tumor.

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

  • TX: primary tumor cannot be assessed

  • T0: no evidence of primary tumor

  • Tis: carcinoma in situ

  • T1: site/tumor specific, generally small

  • T2: site/tumor specific

  • T3: site/tumor specific, generally large

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

  • NX: nodes cannot be assessed

  • N0: no regional nodal metastasis

  • N1: site/tumor specific

  • N2: site/tumor specific

  • N3: site/tumor specific

When tumors 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 tumors of the same histology in the same organ, e.g. T2(m) or T2(5), the latter meaning that there are five primary tumors

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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