Cancer: What do the codes in the doctor’s letter mean?

There is an international system for the classification of cancerous tumors. This helps to describe cancers and compare the results of medical tests and examinations. Doctors and researchers all use what is known as TNM classification.

The abbreviation “TNM” stands for tumor (T), nodes (N), and metastases (M). “Nodes” indicates whether or not the tumor has spread into neighboring (regional) lymph nodes. These are lymph nodes that are located in the drainage area of the affected organ. “Metastases” tells us whether or not the tumor has spread to other parts of the body, forming what is known as distant metastases. So this is what the three letters stand for:

  • T refers to the primary tumor (original tumor).
  • N describes whether or not regional lymph nodes are affected.
  • M describes whether or not distant metastases have been found.

The numbers after the letters indicate how big the tumor is and how far it has spread. The combination of letters and numbers describes the type of cancer, its size, characteristics and extent. Doctors often use this classification as a basis for making a and proposing an individual treatment plan.

Characteristic Abbreviation Meaning
Primary tumor T0 No tumor has been found, or the original tumor cannot be detected (anymore).
  T1 to T4 The numbers 1 to 4 indicate increasing tumor size and extent: T1 describes a small tumor, and T3 describes a bigger tumor, for example.
Lymph nodes N0 There are no tumors in the lymph nodes.
  N1 to N3 The numbers 1 to 3 stand for location and number of affected regional lymph nodes. Tumors found in lymph nodes that are not in the drainage area of the affected organ are regarded as distant metastases.
Metastases M0 No distant metastases have been found.
  M1 There are distant metastases.

Additional details

The following abbreviations may be used in addition to the TNM classification:

  • c (for “clinical”) indicates that the classification is based on physical examination, typical symptoms, or the results of imaging tests, such as ultrasounds and (CT) scans. Clinical classification (cTNM) is usually done before the is confirmed by testing a tissue sample.
  • p (for “pathological”) means that removed tissue was tested in a laboratory, and that the was made based on the results of that test.
  • r (for “recurrence”) means that a tumor has returned.
  • R means that remaining cancer tissue was found after treatment.
  • Tis /Cis describe pre-cancerous changes or early stages of cancer.
  • X indicates that the status of a certain characteristic cannot be determined. This may mean that the necessary medical tests have not been done or that the results are not clear. For example, NX means that it is not possible to determine whether the tumor has spread to the lymph nodes.
  • Y means that the tumor has already been treated.

Grading and staging

Cancer cells are usually less differentiated than healthy cells, and not specialized for a specific task. Grading is used to assess how much the tumor cells differ from healthy cells. It can generally be said that the less differentiated tumor cells are, the faster they grow and the earlier they penetrate surrounding tissue. Tumors are graded using the abbreviations G1 to G4: the higher the grade, the less differentiated and the more malignant the tumor is.

Staging, on the other hand, tells us something about the stage of tumor development. It is based on the results of the medical tests and is done after all the tumor characteristics have been determined. Staging can be of relevance for the of the disease. The most commonly used staging system is that of the International Union against Cancer (UICC). The UICC stages, which range from stage I to stage IV, are determined based on a combination of information from the categories T, N, and M. UICC IV is the most advanced stage.

Not all types of tumors can be classified in this way

The TNM system cannot be used in the same way for all types of cancer. Some tumors may develop in a different way, for example, or other criteria might be more suitable for describing the tumor. There is no primary tumor in leukemia (cancer of the blood), for instance, because blood cancer cells can be found in the entire body right from the onset of the disease. Brain tumors, on the other hand, only rarely spread and form distant metastases. So in leukemia the proportion of abnormal blood cells is important for classification, whereas in brain tumors the degree of cell differentiation () is more relevant.

Andreae. Lexikon der Krankheiten und Untersuchungen. Stuttgart: Thieme. 2008.

International Union against Cancer (UICC). How to use the TNM classification. [Accessed on: April 17, 2011].

Krebsinformationsdienst (KID). Untersuchung bei Krebs: TNM-System und Staging. April 22, 2010 [Accessed on: April 17, 2011].

Kreienberg R, Albert U, Follmann M, Kopp I, Kühn T, Wöckel A et al. Interdisziplinäre S3-Leitlinie für die Diagnostik, Therapie und Nachsorge des Mammakarzinoms: Langversion 3.0. 2012 [Accessed on: August 28, 2012] 

Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J. Harrison’s Principles of internal medicine. New York: McGraw-Hill Companies. 18th ed; 2011.

Pschyrembel W. Klinisches Wörterbuch. Berlin: De Gruyter; 2014.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

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Updated on August 27, 2016
Next planned update: 2021


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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