Understanding Your Stage of Colorectal Cancer

Colorectal cancer starts in the inner lining of the colon or rectum. As colorectal cancer grows, it can grow through the layers of the wall of the colon or rectum. Then, like all cancers, it can spread (metastasize) to other parts of the body. The stage of your cancer is a way health care providers describe how deep and how far your cancer has spread. Knowing the stage is important. The stage is a primary factor in deciding what treatment to use.

Health care providers need to know the stage of your cancer to know what treatment to recommend. The most commonly used system to stage colorectal cancer was developed by the American Joint Committee on Cancer (AJCC). The AJCC system is also called the TNM system. Older staging systems, such as the Dukes and Astler-Coller systems, aren't used much anymore. Because staging is so important for deciding what treatment to use, you should ask your health care provider to explain the stage of your cancer to you in terms you can understand.

The TNM system consists of several different components. Each one is given a score. Then the scores are grouped to determine an overall stage for your cancer. With the TNM system, there are two different types of stages. The first is the clinical stage. Your oncologist will determine this from a physical exam, biopsy, and from imaging tests such as a CT scan, MRI, or PET scan. The clinical stage is used to decide what type of surgery you need. Later, the tissue that is removed during surgery will be examined, and the cancer will be given a new stage called its pathologic stage. This stage will be used to decide what other treatment you might need, if any.

The stage of your cancer is based on the size and extent of your tumor, the number of lymph nodes that are involved, and whether the cancer has spread to distant organs.

The TNM system for colon cancer

The first step in staging your cancer is to decide the individual values for each part of the TNM system. Here's what the letters stand for in the TNM system:

• T tells how far a tumor has spread into the lining of your colon or rectum and nearby tissue.

• N tells whether or not the lymph nodes in the area of the original tumor have become cancerous.

• M tells whether or not the cancer has spread (metastasized) to other distant organs in the body, such as the liver, lung, or lining of your abdomen.

Numerical values are assigned to the T, N, and M categories. There are also two other values that can be assigned. The first is X, which means the doctor does not have enough information to assess the tumor size, lymph node involvement, or metastatic spread. This value is often assigned before surgery. The other value is "in situ." This means the cancer is in its earliest stages and has not spread beyond the first layer of the colon or rectum wall.

Stage groupings

Stage groupings are determined by combining the T, N, and M values from the TNM system. These groupings give an overall description of how advanced your cancer is. A stage grouping can have a value of 0 or a value assigned by a Roman numeral I through IV (1 through 4). The higher the value, the more advanced your cancer is.

These are the stage groupings of colorectal cancer and what they mean:

Stage 0. In this stage, cancer is only in the innermost lining of your colon. It has not spread and is in its earliest stage. This stage is also called carcinoma in situ.

Stage I. In this stage, the cancer has spread to the middle layers of the lining of your colon. It has not spread to the lymph nodes or distant sites. This stage is sometimes called Dukes' A colon cancer.

Stage II. This stage is sometimes called Dukes' B colon cancer. It is divided into three groups:

• Stage IIA. The cancer has grown into the outermost layers of the colon or rectum but has not gone through them. It still has not spread to the lymph nodes or to distant sites.

• Stage IIB. The cancer has grown through the wall of the colon or rectum but has not grown into nearby organs. It has not spread to nearby lymph nodes or distant sites.

• Stage IIC. The cancer has spread outside your colon to nearby tissues or organs. It has still not spread to the lymph nodes or to distant sites.

Stage III. This stage is sometimes called Dukes' C colon cancer. It is divided into three groups: 

• Stage IIIA. One of the following applies:

  • The cancer has spread to the first or middle layers of your colon or rectum wall and has also spread to one to three lymph nodes. It hasn't spread to distant sites, though.

  • The cancer has grown into the first layer of the colon or rectum wall and has also spread to four to six nearby lymph nodes. It hasn't spread to distant sites. 

• Stage IIIB. One of the following applies:

  • The cancer has grown into or through the outer layers of the colon or rectum but hasn't spread to nearby organs. It has spread to one to three nearby lymph nodes. It has not spread to distant sites.

  • The cancer has grown into the middle or outer layers of the colon or rectum and has spread to four to six nearby lymph nodes. It hasn't spread to distant sites.

  • The cancer has grown into the first or middle layers of the colon or rectum, and has spread to seven or more nearby lymph nodes. It hasn't spread to distant sites.

• Stage IIIC. One of the following applies:

  • The cancer has grown through the outer layers of the colon or rectum but hasn't reached nearby organs. It has spread to four to six nearby lymph nodes, but not to distant sites.

  • The cancer has grown into or through the outer layers of the colon or rectum but hasn't reached nearby organs. It has spread to seven or more nearby lymph nodes, but not to distant sites.

  • The cancer has grown into or through the outer layers of the colon or rectum and has reached nearby organs. It has spread to one or more nearby lymph nodes or into areas of fat near the lymph nodes, but not to distant sites.

Stage IV. This stage is sometimes called Dukes' D colon cancer. This stage is divided into two sub-stages:

• Stage IVA. The cancer may or may not have grown through the wall of the colon or rectum, and it may or may not have reached nearby lymph nodes. It has spread to one distant organ (such as the lungs or liver) or one distant set of lymph nodes.

• Stage IVB. The cancer may or may not have grown through the wall of the colon or rectum, and it may or may not have reached nearby lymph nodes. It has spread to more than one distant organ (such as the liver or the lungs) or set of distant lymph nodes, or it has spread to distant parts of the peritoneum (the lining of the abdominal cavity).