Staging Cancer using TNM

If you know someone diagnosed with cancer, it may even be you, then you’ve heard the term ‘staging’ or stages. What exactly do these stages indicate and how are they determined?

What is staging?

Staging helps describe where a cancer is located, if or where it has spread, and whether it is affecting other parts of the body. Doctors often use diagnostic tests to determine a cancer’s stage. Staging may not be complete until all of these tests are finished. Knowing the stage of the cancer helps the doctor to:

• Plan treatment, including the type of surgery and/or whether chemotherapy or radiation therapy are needed
• Predict the chance that the cancer will come back after the original treatment
• Predict the chance of recovery
• Talk about the diagnosis in a clear, common language with the entire health care team
• Determine how well the treatment worked
• Compare how well new treatments work among large groups of people with the same diagnosis

Understanding the TNM staging system doctors use

For most types of cancer, doctors most frequently use the TNM system of the American Joint Committee on Cancer (AJCC) to describe a cancer’s stage. Doctors answer the following questions based on the results from diagnostic tests, imaging scans, and surgery to remove or get a sample of the tumor.

• Tumor, T – How large is the primary tumor and where is it located?
• Node, N – Has the tumor spread to the lymph nodes? If so, where and how many nodes are affected?
• Metastisis, M – Has the cancer spread to other parts of the body? If so, where and how much?
• Are there any biomarkers or tumor markers linked to the cancer that may make it more or less likely to spread?

TNM descriptions

These are the general descriptions of the TNM staging system. Keep in mind that the specific definitions for each category are different for each type of cancer that is staged using this system.

• Tumor (T). The letter “T” plus a number (0 to 4) describes the size and location of the tumor, including how much the tumor has grown into nearby tissues. Tumor size is measured in centimeters (cm). A centimeter is roughly equal to the width of a standard pen or pencil. A larger tumor or a tumor that has grown more deeply into the surrounding tissue receives a higher number. For some types of cancer, lowercase letters, such as “a,” “b,” or “m” (for multiple), are added to the “T” category to provide more detail.
• Node (N). The letter “N” plus a number (0 to 3) stands for lymph nodes. These tiny, bean-shaped organs help fight infection. Lymph nodes near where the cancer started are called regional lymph nodes. Lymph nodes in other parts of the body are called distant lymph nodes. Most often, the more lymph nodes with cancer, the larger the number assigned. However, for some tumors, the location of the lymph nodes with cancer may determine the “N” category.
• Metastasis (M). The letter “M” indicates whether the cancer has spread to other parts of the body, called distant metastasis. If the cancer has not spread, it is labeled M0. If the cancer has spread, it is considered M1.

In addition to the TNM categories, other factors may be included in the stage depending on the specific type of cancer. These may include tumor markers or bio-markers, grade, and tumor genetics.

Cancer Stage Grouping

Doctors will combine the T, N, M results and other factors specific to the type of cancer to determine the stage for each person. Most types of cancer have four stages: stages I (1) to IV (4). Some cancers also have a stage 0 (zero).

• Stage 0. This stage describes cancer in situ, which means “in place.” Stage 0 cancers are still located in the place they started and have not spread to nearby tissues. This stage of cancer is often highly curable, usually by removing the entire tumor with surgery.
• Stage I. This stage is usually a small cancer or tumor that has not grown deeply into nearby tissues. It also has not spread to the lymph nodes or other parts of the body. It is often called early-stage cancer.
• Stage II and Stage III. In general, these 2 stages indicate larger cancers or tumors that have grown more deeply into nearby tissue. They may have also spread to lymph nodes but not to other parts of the body.
• Stage IV. This stage means that the cancer has spread to other organs or parts of the body. It may also be called advanced or metastatic cancer.

Restaging a cancer

The stage of a cancer does not change over time. If the cancer comes back or spreads to another part of the body, the more recent information about the size and spread of the cancer is added to the original stage.

Sometimes, a doctor might “restage” a cancer to determine how well a treatment is working or to get more information about a cancer that has come back after treatment. This process uses the same staging system described above. Usually some of the same tests that were done when the cancer was first diagnosed will be repeated.

After this, the doctor may assign the cancer a new stage. The doctor then adds a lowercase “r” before the new stage to show that it is different from that of the first diagnosis. However, this is not common.

Other staging systems

The TNM system is mainly used to describe cancers that form solid tumors, such as breast, colon, and lung cancers. However, doctors use other staging systems to classify other types of cancer, such as:

• Central nervous system tumors (brain tumors). Because cancerous brain tumors do not normally spread outside the brain and spinal cord, only the “T” description of the TNM system applies. Currently, no single staging system exists for central nervous system tumors.
• Childhood cancers. The AJCC does not include childhood cancers in its staging system. Doctors stage most childhood cancers separately according to other staging systems that are often specific to the type of cancer.
• Cancers of the blood. The TNM system does not describe leukemia, lymphoma, or multiple myeloma since they usually do not form solid tumors. Each blood cancer has a unique staging system.

Further Reading and Patient Care