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

There is an international system for the classification of cancerous tumors. Known as TNM classification, it helps doctors and researchers to describe cancers and compare the results of medical tests and examinations.

The abbreviation “TNM” stands for tumor (T), nodes (N), and metastases (M). “Nodes” indicates whether or not the tumor has spread into nearby (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 mean:

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 of spreading. Doctors often use this classification as a basis for making a prognosis and suggesting an individual treatment plan.

Characteristic	Abbreviation	Meaning
Primary tumor	T0	No tumor has been found, or the original tumor can't be detected (anymore).
	T1 to T4	The numbers 1 to 4 indicate increasing tumor size and extent of spreading: 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 describe the location and number of affected regional lymph nodes. Tumors found in lymph nodes that aren't in the drainage area of the affected organ are considered to be distant metastases.
Metastases	M0	No distant metastases have been found.
	M1	There are distant metastases.

Additional details

The following abbreviations are sometimes used in addition to the TNM classification:

c (for “clinical”) indicates that the classification is based on a physical examination, typical symptoms, or the results of imaging tests. These include ultrasounds and computed tomography (CT) scans. This clinical classification (cTNM) is usually done before the diagnosis is confirmed by testing a tissue sample.
p (for “pathological”) means that removed tissue was tested in a laboratory, and that the tumor was classified 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 cell changes or early stages of cancer.
X indicates that the status of a certain characteristic can't be determined. This may mean that the necessary medical tests haven't been done or that the results aren't clear. For example, NX means that it's not possible to say whether the tumor has spread to lymph nodes.
Y means that the tumor has already been treated.

Grading and staging

Cancer cells are usually less developed (differentiated) than healthy cells, and not specialized for a specific task. Grading is done to assess how much the tumor cells differ from healthy cells. In many cases, the less differentiated tumor cells are, the faster they grow and the earlier they spread to 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 influence the prognosis 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 can't 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 start 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 (grading) is more relevant.

Krebsinformationsdienst (KID). Arztbriefe, Krankenakte: Befunde und Abkürzungen verstehen. 2017.

Pschyrembel Online. 2021.

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. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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

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Updated on April 25, 2022

Next planned update: 2025

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

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