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Classifying colorectal cancer into different stages of disease provides information about patients' prognosis and treatment options. Knowing how deep the tumor extends through the gastrointestinal tract, whether the cancer has spread to local lymph nodes, and if the cancer is metastatic is critical to determine the stage. The stages of colorectal cancer range from 0 to IV, with IV representing the most severe disease.
Determining the stage of colorectal cancer requires knowing three important pieces of information about the tumor. First, it is important to know the tumor's depth of penetration through the gastrointestinal tract. Information about whether the cancer has spread to regional lymph nodes is also critical in the staging process. The third piece of information is whether the tumor has spread to distant locations in the body through a process called metastasis. These three characteristics are often referred to by the acronym TNM, where T stands for the primary tumor, N stands for whether disease is present in nodes, and M stands for whether metastases are present.
The stages of colorectal cancer are determined based on information from the TNM analysis. Colorectal cancer is classified as stage 0, I, II, III, or IV. Stage IV represents the most severe cancer, while stage 0 disease is the least extensive. Detailed charts are available that list the specific TNM characteristics that classify different cancers into these stages; the charts were developed by researchers who studied the outcomes of patients with different types of cancers.
Stage 0 colorectal cancer describes tumors that do not penetrate very far into the wall of the gastrointestinal tract. Another term for these growths is “carcinoma-in-situ.” With this cancer, there are no metastases or spread to local lymph nodes. Prognosis for this type of cancer is excellent, and most patients are cured by surgery alone.
Similar to patients with stage 0, patients with stage I disease do not have spread of the cancer to lymph nodes or distant parts of the body. At this stage, however, the cancer does extend further into the wall of the gastrointestinal tract. These patients still have a good prognosis, and their five-year survival rate is approximately 93%.
With stage II, even deeper extension of the tumor is seen. In these patients, the cancer can grow completely through the wall of the gastrointestinal tract. There are still no metastases or spread to local lymph nodes, however.
Out of the stages of colorectal cancer, stage III has the most variability. Different depths of cancer penetration at the site of the initial tumor are seen. All patients in this stage have some amount of cancer in their local lymph nodes. Patients in stage III have a different prognosis depending on their TNM characteristics, but five-year survival ranges from 44-83%.
Stage IV of the stages of colorectal cancer has the worst prognosis. All patients given this stage classification have metastases of the cancer to distant locations. Often these patients have limited treatment options, and might not even receive surgery to remove the cancer because this procedure would do more harm than good. Treatment options such as chemotherapy or radiation therapy can sometimes be offered to these patients.