|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.|
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.