The most common system for staging a cancer that is a solid tumor is the TNM system. Most providers and cancer centers use it to stage most cancers. The TNM system is based on:
- The size of the primary tumor (T)
- How much cancer has spread to nearby lymph nodes (N)
- Metastasis (M), or if and how much the cancer has spread to other areas in the body
Numbers are added to each category that explains the size of the tumor and how much it has spread. The higher the number, the greater the size and the more likely cancer has spread.
Primary Tumor (T):
- TX: The tumor cannot be measured.
- T0: The tumor cannot be found.
- Tis: Abnormal cells have been found, but have not spread. This is called carcinoma in situ.
- T1, T2, T3, T4: Indicate the size of the primary tumor and how much it has spread into surrounding tissue.
Lymph Nodes (N):
- NX: Lymph nodes cannot be evaluated
- N0: No cancer found in nearby lymph nodes
- N1, N2, N3: Number and location of lymph nodes involved where cancer has spread
Metastasis (M):
- MX: Metastasis cannot be evaluated
- M0: No metastasis found (cancer has not spread)
- M1: Metastasis is found (cancer has spread to other parts of the body)
As an example, a bladder cancer T3 N0 M0 means there is a large tumor (T3) that has not spread to lymph nodes (N0) or anywhere else in the body (M0).
Sometimes other letters and sub-categories are used in addition to the ones above.
A tumor grade, such as G1-G4 can also be used along with staging. This describes how much cancer cells look like normal cells under a microscope. Higher numbers indicate more abnormal cells. The less the cancer looks like normal cells, the faster it will grow and spread.
Not all cancers are staged using the TNM system. This is because some cancers, particularly blood and bone marrow cancer such as leukemia, do not form tumors or spread in the same way. So other systems are used to stage these cancers.