Understanding cancer staging
Cancer staging is a way to describe how much cancer is in your body and where it is located in your body. Staging helps determine where the original tumor is, how big it is, whether it has spread, and where it has spread.
Cancer staging can help your health care provider:
- Determine your prognosis (chance of recovery or likelihood the cancer will come back)
- Plan your treatment
- Identify clinical trials you may be able to join
Staging also gives providers a common language to use to describe and discuss cancer.
Cancer is the uncontrolled growth of abnormal cells in the body. These cells often form a tumor. This tumor can grow into the surrounding tissues and organs. As the cancer progresses, cancer cells from the tumor can break away and spread to other parts of the body through the bloodstream or lymph system. When cancer spreads, tumors can form in other organs and parts of the body. The spread of cancer is called metastasis.
Cancer staging is used to help describe the progression of cancer. It is often defined by:
- Location of the primary (original) tumor and type of cancer cells
- Size of the primary tumor
- Whether the cancer has spread to lymph nodes
- Number of tumors from the cancer that has spread
- Tumor grade (how much cancer cells look like normal cells)
To assess your cancer, your provider may perform different tests, depending on where the cancer is in your body. These may include:
- Imaging tests, such as x-rays, CT scans, PET scans, or MRIs
- Lab tests
You also may have surgery to remove the cancer and lymph nodes or to explore the cancer in your body and take a tissue sample. These samples are tested and can provide more detailed information about the cancer stage.
TNM Staging System
The most common system for staging cancer in the form of 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
- 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 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.
Assigning a Stage
A stage is assigned to your cancer based on the TNM values and other factors. Different cancers are staged differently. For instance, stage III colon cancer is not the same as a stage III bladder cancer. In general, a higher stage refers to more advanced cancer.
- Stage 0: Abnormal cells are present, but have not spread
- Stage I, II, III: Refer to size of tumor and how much cancer has spread to lymph nodes
- Stage IV: Disease has spread to other organs and tissues
Once your cancer has been assigned a stage, it does not change, even if the cancer does come back. A cancer is staged based on what is found when it is diagnosed.