What is the TNM system?

The TNM system is one of the most widely used cancer staging systems. This system has been accepted by the Union for International Cancer Control (UICC) and the American Joint Committee on Cancer (AJCC). Most medical facilities use the TNM system as their main method for cancer reporting.

The TNM system is based on the size and/or extent (reach) of the primary tumor (T), the amount of spread to nearby lymph nodes (N), and the presence of metastasis (M) or secondary tumors formed by the spread of cancer cells to other parts of the body. A number is added to each letter to indicate the size and/or extent of the primary tumor and the degree of cancer spread.

Primary Tumor (T)
TX: Primary tumor cannot be evaluated
T0: No evidence of primary tumor
Tis: Carcinoma in situ (CIS; abnormal cells are present but have not spread to neighboring tissue; although not cancer, CIS may become cancer and is sometimes called preinvasive cancer)
T1, T2, T3, T4: Size and/or extent of the primary tumor


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Regional Lymph Nodes (N)
NX: Regional lymph nodes cannot be evaluated
N0: No regional lymph node involvement
N1, N2, N3: Degree of regional lymph node involvement (number and location of lymph nodes)

Distant Metastasis (M)
MX: Distant metastasis cannot be evaluated
M0: No distant metastasis
M1: Distant metastasis is present

For example, breast cancer classified as T3 N2 M0 refers to a large tumor that has spread outside the breast to nearby lymph nodes but not to other parts of the body. Prostate cancer T2 N0 M0 means that the tumor is located only in the prostate and has not spread to the lymph nodes or any other part of the body.

For many cancers, TNM combinations correspond to one of five stages. Criteria for stages differ for different types of cancer. For example, bladder cancer T3 N0 M0 is stage III, whereas colon cancer T3 N0 M0 is stage II.

Stage Definition
Stage 0 Carcinoma in situ
Stage I, Stage II, and Stage III Higher numbers indicate more extensive disease: Larger tumor size and/or spread of the cancer beyond the organ in which it first developed to nearby lymph nodes and/or tissues or organs adjacent to the location of the primary tumor
Stage IV The cancer has spread to distant tissues or organs

Are all cancers staged with TNM classifications?

Most types of cancer have TNM designations, but some do not. For example, cancers of the brain and spinal cord are staged according to their cell type and grade. Different staging systems are also used for many cancers of the blood or bone marrow, such as lymphomas. The Ann Arbor staging classification is commonly used to stage lymphomas and has been adopted by both the AJCC and the UICC. However, other cancers of the blood or bone marrow, including most types of leukemia, do not have a clear-cut staging system. Another staging system, developed by the International Federation of Gynecology and Obstetrics (FIGO), is used to stage cancers of thecervix, uterus, ovary, vagina, and vulva. This system is also based on TNM information. Additionally, most childhood cancers are staged using either the TNM system or the staging criteria of the Children’s Oncology Group (COG), which conducts pediatric clinical trials; however, other staging systems may be used for some childhood cancers.

Many cancer registries, such as those supported by NCI’s Surveillance, Epidemiology, and End Results (SEER) Program, use “summary staging.” This system is used for all types of cancer. It groups cancer cases into five main categories:

  • In situ: Abnormal cells are present only in the layer of cells in which they developed
  • Localized: Cancer is limited to the organ in which it began, without evidence of spread
  • Regional: Cancer has spread beyond the primary site to nearby lymph nodes or tissues and organs
  • Distant: Cancer has spread from the primary site to distant tissues or organs or to distant lymph nodes
  • Unknown: There is not enough information to determine the stage