After a diagnosis of colon cancer, the cancer is staged. Staging is a standardized way of describing the extent and spread of the cancer, which helps guide treatment plans and prognosis. The American Cancer Society describes the American Joint Committee Cancer (AJCC) staging system as the staging typically used for colon cancer. The AJCC staging uses a TNM, or tumor, nodes and metastases, categorization. These categories describe how big or how far the tumor has extended, whether any lymph nodes are involved, and if distant sites are cancerous. Numbers after the letters TNM range from 0 to 4, with 4 being the most severe. If there is an "X" instead of a number, it means the information cannot be determined.
Stage 0 (Carcinoma in Situ)
Stage 0 colon cancer is classified as Tis, N0, M0, according to the American Cancer Society. This is the earliest stage of colon cancer, and means that cancer is only in the in layer of the colon. It may also be called carcinoma in situ. No cancer is in the lymph nodes (N0) and there are no metastases (M0).
Stage I
Stage I colon cancer is T1-T2, N0, M0. Cancer has grown through the muscle tissue layer of the colon and into the submucosa, which is fibrous tissue under the muscle tissue (T1) or it has grown through the submucosa into the thicker outer muscle layer that helps the intestines contract (T2). There is no cancer in the lymph nodes and no metastases.
Stage II
The second stage of colon cancer has several sub-stages. Stage IIA colon cancer is classified as T3, N0, M0; this involves cancer that has spread to the outer layers of the colon but has not spread through all the layers. The lymph nodes and distant sites are cancer-free. Stage IIB is colon cancer that is T4a, N0, M0. This is cancer that has spread through the outer colon layers but has not reached nearby organs, and there are no cancerous lymph nodes or metastases. The last sub-stage of Stage II, Stage IIC, describes cancer that has not only spread through the outer layer of the colon, but has also attached to or grown into nearby organs. Despite this growth, no lymph nodes are involved and there are no metastases.
Stage III
There are three sub-stages in Stage III colon cancer. Stage IIIA can involve T1-T2, N1, M0 (similar to Stage I cancer, but with the involvement of one to three lymph nodes or fat near the lymph nodes); or it may be T1, N2a, M0, which means the cancer is in the submucosa and has also been found in four to six nearby lymph nodes.
Stage IIIB can describe colon cancer that is either T3-T4a, N1, M0, which means the cancer has spread to the outer layers of the colon or through the lining of the stomach (peritoneum) but is not in other organs and is also in one to three lymph nodes or fat around lymph nodes; T2-T3, N2a, M0, which means the cancer has spread to either the muscular layer or the outer layer of the colon and has also been found in four to six lymph nodes; or T1-T2, N2b, M0, which means the cancer has spread to the submucosa or muscular layer of the colon and is also in seven or more lymph nodes.
Stage IIIC colon cancer can be T4a, N2a, M0, which is cancer that has spread through the colon to the peritoneum but has not been found in other organs and has spread to four to six lymph nodes; T3-T4a, N2b, M0, meaning the cancer has spread to the outer layers of the colon OR to the peritoneum and is in seven or more lymph nodes; or T4b, N1-2, M0, which describes cancer that has spread through the outer layer of the colon and is in or attached to other organs or tissues, and is also in one or more lymph nodes.
None of the Stage III cancers have distant metastases.
Stage IV
The last stage of colon cancer, Stage IV, has two sub-stages. Stage IVA is diagnosed as any T, any N, and M1a, which means the cancer may have spread through all of the layers of the colon or not, lymph nodes may or may not be involved, and it has spread to one other distant organ like the lungs. Stage IVB is any T, any N, and M1b, which is the same as IVA, except in this sub-stage, colon cancer has been found in more than one distant part of the body, distant lymph nodes, or distant parts of the stomach lining.
