Colon cancer, which is sometimes also called colorectal cancer, is the third leading cause of cancer-related deaths in the country. The disease begins in the large intestine (colon), and it can spread to other parts of the body. Patients who have colon cancer often report regular changes in bowel movement, weakness or fatigue, and unexplained weight loss. Rectal bleeding is also commonly experienced.

Timely medical treatment can help reduce the severity of these symptoms. Before proceeding with the treatment plan, the doctor performs specific tests to understand the stage of cancer. Read on to know the different stages involved in colon cancer.

TNM staging system
Doctors use the TNM staging system to learn the stage of colon cancer. The system reveals three key details:

1. Tumor (T)
This part of the TNM staging system helps the doctor know the extent to which the tumor has grown. TX, Tis, T1, and T4a are a few metrics that can provide detailed information of the tumor’s location.

2. Node (N)
Lymph nodes are present throughout the body. They contain cells that help the body fight infections. Lymph nodes are present near the rectum and colon, and they’re called regional lymph nodes. The TNM staging system also provides insight into the tumor cells’ spread to different regional lymph nodes.

3. Metastasis (M)
Distant metastasis is the last of the three parameters of the TNM staging system. It helps the doctor know if cancer has spread to other organs as well.

Stages of colon cancer
By evaluating the results of the TNM staging system, doctors can determine the stage of colon cancer. In total, the disease proceeds through five stages:

1. Stage 0
Also called cancer in situ, stage 0 is the first stage of colon cancer. In this stage, the tumor is restricted to the mucosa, which is the innermost lining of the colon or rectum.

2. Stage I
This is the stage where the cancer cells have spread from the mucosa to the submucosa, which is the next layer of the colon.

3. Stage II
Stage II is more complicated than stage I, with the disease spreading beyond the mucosa and submucosa. That is why this stage is further classified into three stages, which are:

• Stage IIA
  In this stage, the cancer cells have breached the walls of the colon without affecting any organs or the lymph nodes.
• Stage IIB
  This stage is confirmed when the tumor reaches the walls of the abdomen, called the visceral peritoneum. The lymph nodes are not affected in this stage.
• Stage IIC
  Other organs are affected in this stage of colon cancer.

4. Stage III
This stage is also divided into three stages: stage IIIA, stage IIIB, and stage IIIC. In IIIA, the tumor is found in nearby lymph nodes, but not distant organs. In IIIB, the tumor penetrates up to three lymph nodes, while in IIIC, it spreads to four or more lymph nodes.

5. Stage IV
Stage IVA and IVB are two subdivisions of stage IV of colon cancer. Stage IVA indicates that the tumor has spread to the lung or liver, while IVB is the most advanced stage where the tumor spreads to multiple other organs.