Treatments and diagnostic tests

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 prognosis 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 computed tomography (CT) scans. 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 diagnosis 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 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 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 (grading) is more relevant.