The severity of any cancer is determined by clinical staging. This maxim holds true for colon, or colorectal, cancer. There are numerous tests listed by the American Cancer Society that aid in the staging of colon cancer. These tests include PET, CT or MRI scans of the abdomen, chest or brain. Staging represents how much the cancer has penetrated the wall of the colon, if the cancer has spread to nearby structures and whether or not the lesions have spread to distant organs or lymph nodes.
Stage 0
The National Cancer Institute lists stage 0 colon cancer as abnormal cells that are only found on the innermost layer of the colon. This type of lesion is termed carcinoma in situ. Doctors may term stage 0 as a precancerous lesion, because the mass has yet to invade any layer of the colon. However, if left untreated, it always progresses to a higher stage of cancer.
Stage 1
Colon cancer that is classified as stage 1 is cancer that has formed a mass that extends past the innermost levels of the colon and has reached the middle layers. These layers are the muscularis mucosa, the submucosa and the muscularis propria, explains the American Cancer Society. The cancer at this stage has yet to spread to any lymph nodes.
Stage 2
The American Cancer Society divides stage 2 colorectal cancers into two levels. The two levels are 2A and 2B. Stage 2A colon cancer is when the cancer has reached the deepest layers of the colon, but it has yet to reach the nearby structures surrounding the colon. Stage 2B colon cancer is when the cancer has penetrated the deepest layers of the colon. In this stage, there may be some spread to nearby structures, but no lymph nodes have been affected.
Stage 3
MedlinePlus establishes stage 3 colorectal cancer as cancer that has spread to nearby lymph nodes. The National Cancer Institute divides stage 3 cancer into three levels: stage 3A, stage 3B and stage 3C. Stage 3A is when the cancer has broken through the layers of the colon and spread to at least three lymph nodes. Stage 3B is when the cancer has affected three lymph nodes and spread to the tissues surrounding the colon. The final level, stage 3C, is when the cancer has affected four lymph nodes and spread to the covering of the abdominal cavity. This covering is called the peritoneum.
Stage 4
Stage 4 cancer is the most dangerous stage of cancer. The American Cancer Society divides this stage into stages 4A and 4B. Cancer is classified as stage 4A when the cancer has yet to penetrate through the levels of the colon, but it has spread to one distant organ, such as the liver or the lungs, or one set of lymph nodes. Stage 4B cancer is when the cancer has spread to more than one distant organ or more than one set of lymph nodes. Colon cancer that has spread to both the liver and the brain is stage 4B cancer. The prognosis for this type of cancer is very poor.
