The process of analyzing all the pertinent information and assigning your disease to a particular group, or stage, is called staging.
Not all colorectal cancers will be treated the same way. The therapy will be adjusted to each individual cancer and situation. To help determine who should get what treatment, cancer specialists rely on staging—a system that places the cancer into a certain group. The stage of your tumor is the most important factor in deciding what type of treatment is best for you.
Clinical staging is the initial and tentative staging that is based on the results of the physical exam and the diagnostic tests performed before surgery. These may include others such as liver function tests to make sure the liver is functioning well and a chest x-ray to make sure the tumor has not spread to the lungs.
The final determination of the stage, called pathological staging, will come after the surgeon had an opportunity to examine the inside of the abdomen during the procedure, and the tumor has been removed surgically and examined under a microscope.
Today, the TNM—tumor, node, metastasis—staging system, which places patients into one of four stages (Stage I-IV), is the common method. This system is based on: the depth of invasion of the tumor; the presence of cancer cells in the lymph nodes; and metastasis, or spread, to other organs.
Tumor depth of invasion (T) is determined when the tumor is removed and sent to the pathologist.
Lymph nodes (N) are checked for tumor spread at the time of surgery. A minimum of twelve nodes is needed for an accurate assessment.
Metastasis, or spread to other organs (M), is assessed with x-rays, scans, and blood tests.
The pathologist will examine the specimen removed during surgery, review other information, and assign a rating to each of the three letters.
The exact rating is very detailed. For example T1 is a cancer that has grown through the muscularis mucosa and extends into the submucosa. A T4b cancer has grown through the wall of the colon or rectum and is attached to or invades nearby tissues. N1b means cancer cells are found in two to three nearby lymph nodes. And M1a indicates that the cancer has spread to 1 distant organ or set of distant lymph nodes.
All the ratings are assembled to determine the stage of the tumor. For example, a T1 tumor (one that has not spread beyond the submucosa layer of the bowel), that is N0 (no nodes have been invaded by cancer) and M0 (there is no evidence of spread to other organs) is labeled T1 N0 M0. By refering to staging tables, this tumor is staged as stage I.
The stage, in turn will guide the medical team in selecting the appropriate therapy. The extent of the treatment will be matched to the extent of spread of the disease. The more extensive the spread, the more intense the treatment.
You may find it helpful to think of stage as degree of risk presented by a particular tumor. At one end of the scale are the low-risk situations: very tiny tumors that have not spread through the bowel wall. Further along are slightly larger tumors that have penetrated the bowel wall. At the other end of the scale are tumors that have invaded the lymph nodes or spread to other parts of the body.
If you are at the low risk end of the scale, your treatment may require only surgical removal of the tumor. More advanced tumors may be treated with more extensive surgery and aggressive additional therapy. The next section goes into greater detail about making treatment choices.
Stage 0: Tis, N0, M0
The cancer is in the earliest stage, carcinoma in situ.
Stage I: T1 N0 M0; T2 N0 M0
Cancer has begun to spread, but has not spread to nearby lymph nodes.
Stage IIA: T3 N0 M0
The cancer has grown into the outermost layers of the bowel.
Stage IIB: T4a N0 M0
The cancer has grown through the wall of the colon or rectum.
Stage IIC: T4b N0 M0
Cancer has spread to other organs near the colon or rectum. It has not reached the lymph nodes.
Stage IIIA: T1-T2, N1, M0
Spread to the lymph nodes, but not to distant parts of the body.
Stage IIIB: T3-T4a, N1, M0 or T2-T3, N2a, M0 or T1-T2, N2b, M0
Cancer has grown into the outermost layers but has not reached nearby organs.
Stage IIIC: T4a, N2a, M0, or T3-T4a, N2b, M0, or T4b, N1-N2, M0
Cancer has reached nearby organs but has not spread to distant sites.
Stage IVA: any T, any N, M1a
Spread to one distant organ or one set of lymph nodes.
Stage IVB: any T, any N, M1b
Most advanced cancer that has spread to several distant parts of the body, such as liver and lungs.
* This is a very simplified version. For a complete description, check
out the latest American Joint Committee on Cancer (AJCC) staging