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TNM staging

The TNM classification system describes the extent of many types of solid tumour cancers. It gives doctors a common language to describe a cancer. The Union for International Cancer Control (UICC) and the American Joint Committee on Cancer (AJCC) both use the TNM classification system to describe the extent of many solid tumour cancers.

TNM is based on 3 components:

LetterStands forDescription



indicates the size of the primaryprimaryThe site or area in the body where cancer started. tumour and the degree of spread into nearby tissues (local invasion)


lymph nodes

indicates whether or not the cancer has spread to nearby lymph nodes, the size of the nodes that contain cancer and how many lymph nodes contain cancer



indicates whether or not cancer has spread (metastasized) to distant organs

Additional letters or numbers are placed after T, N and M to provide more specific details:

  • X means the tumour or lymph nodes cannot be assessed or evaluated.
  • T followed by a number (0–4) describes the size of tumour and how much nearby tissue it has invaded.
  • N followed by a number (0–3) describes the degree of spread to the lymph nodes.
  • M followed by the number 0 or 1 describes whether or not cancer has spread to other parts of the body.
  • Lowercase letters (a, b or c) are used to subdivide the tumour, lymph nodes or metastasis categories to make them more specific.

Primary tumour (T)


primary tumour cannot be assessed


no evidence of primary tumour


carcinoma in situcarcinoma in situA very early stage of cancer in which tumour cells have not yet invaded surrounding tissues.

T1, T2, T3 or T4

The number corresponds to the size of the primary tumour and how far it has spread. The higher the number, the larger the tumour and the greater the spread to nearby structures and tissue.

Regional lymph nodes (N)


regional lymph nodes cannot be assessed


no evidence that regional lymph nodes are involved

N1, N2 or N3

the number corresponds to the degree of spread of cancer to the regional lymph nodes

Note: If the primary tumour extends into nearby lymph nodes (regional lymph nodes), it is considered a lymph node metastasis. Metastasis in any other group of lymph nodes is usually considered distant metastasis.

Distant metastasis (M)


no evidence of distant metastasis


distant metastasis is present

The TNM staging system varies from one type of cancer to another.

Clinical and pathological TNM classifications

Solid tumours are usually given both clinical and pathological TNM classifications.

  • The clinical TNM classification is given before treatment. It is assigned based on the results of diagnostic tests.
  • The pathological TNM classification (pTNM) is based on examination of the tumour and other tissues after they are surgically removed. Pathological classification is clearly noted by the addition of the letter p to the T, N or M component. The pTNM corresponds to the TNM categories.

The pathological classification is more accurate in assessing tumour size and spread to the lymph nodes than the clinical classification. However, the pathological classification often cannot take into consideration other variables like distant metastasis. To arrive at the most accurate staging, both pathological and clinical staging have to be taken into consideration.


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