As colorectal cancer grows, it can spread through 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 doctors 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.
Doctors need to know the stage of your cancer to know what treatment to recommend. There are 3 different systems doctors use for staging colorectal cancer. They are Dukes, Astler-Coller, and AJCC, which stands for American Joint Committee on Cancer. The AJCC, which is the most commonly used system for staging, is also called the TNM System. It is the system we describe here. Because staging is so important for deciding what treatment to use, you should ask your doctor 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 and from imaging tests such as a CT 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 your 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 (is)." 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 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 2 groups.
Stage IIA. In this stage, the cancer has spread outside the middle layers of your colon wall or it has spread to tissues near your colon or rectum. It still has not spread to the lymph nodes or to distant sites.
Stage IIB. The cancer has spread outside your colon to nearby organs. Or it may have spread to the tissue that lines your abdominal wall, called the peritoneum. It still has not spread to the lymph nodes or to distant sites.
Stage III. Stage III is sometimes called Dukes' C colon cancer. It is divided into three sub-stages--stage IIIA, stage IIIB, and stage IIIC.
Stage IIIA. The cancer has spread to the middle layers of your colon wall and has also spread to one to three lymph nodes. It hasn't spread to distant sites though.
Stage IIIB. This means the cancer has spread beyond the middle tissue layers of the colon wall, or to nearby tissues around the colon or rectum and to as many as three lymph nodes. It may also have spread into nearby organs or through the peritoneum or both. It still hasn't spread to distant sites.
Stage IIIC. The cancer has spread to four or more nearby lymph nodes but not yet to distant sites.
Stage IV. This stage is sometimes called Dukes' D colon cancer. In this stage, cancer may have spread to nearby lymph nodes and has spread to distant sites in the body, such as the liver, lungs, or ovary.
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