If you’ve been diagnosed with colon cancer, one of the first things your doctor will want to determine is the stage of your cancer. The stage refers to the extent of the cancer or how far it has spread. Staging colon cancer is essential to determine the best treatment approach.

Colon cancer is typically staged based on a system established by the American Joint Committee on Cancer called the TNM staging system.

The system considers the following factors:

  • Primary tumor (T). Primary tumor refers to how large the original tumor is and whether cancer has grown into the wall of the colon or spread to nearby areas.
  • Regional lymph nodes (N). Regional lymph nodes refer to whether cancer cells have spread to nearby lymph nodes.
  • Distant metastases (M): Distant metastases refers to whether cancer has spread from the colon to other parts of the body, such as the lungs or liver.

Within each category, the disease is classified even further and assigned a number or a letter to indicate the extent of the disease. These assignments are based on the structure of the colon, as well as how far the cancer has grown through the layers of the colon wall.

The stages of colon cancer are as follows:

Stage 0

This is the earliest form of colon cancer and means it has not grown beyond the mucosa, or the innermost layer of the colon.

Stage 1

Stage 1 colon cancer indicates the cancer has grown into the inner layer of the colon, called the mucosa, to the next layer of the colon, called the submucosa. It has not spread to the lymph nodes.

Stage 2

In stage 2 colon cancer, the disease is a little more advanced than stage 1 and has grown beyond the mucosa and the submucosa of the colon. Stage 2 colon cancer is classified further as stage 2A, 2B, or 2C.

  • 2A stage. The cancer has not spread to the lymph nodes or nearby tissue. It has reached the outer layers of the colon. But it has not completely grown through.
  • 2B stage. The cancer has not spread to the lymph nodes, but has grown though the outer layer of the colon and to the visceral peritoneum. This is the membrane that holds the abdominal organs in place.
  • 2C stage. The cancer is not found in nearby lymph nodes, but in addition to growing through the outer layer of the colon, it has grown to nearby organs or structures.

Stage 3

Stage 3 colon cancer is classified as stage 3A, 3B, and 3C as follows:

  • 3A stage. The tumor has grown to or through the muscular layers of the colon and is found in nearby lymph nodes. It has not spread to distant nodes or organs.
  • 3B stage. The tumor has grown through the outmost layers of the colon and penetrates the visceral peritoneum or invades other organs or structures and is found in one to three lymph nodes. Or the tumor is not through the outer layers of the colon wall but is found in 4 or more nearby lymph nodes.
  • 3C stage. The tumor has grown beyond the muscular layers and cancer is found in four or more nearby lymph nodes, but not distant sites.

Stage 4

Stage 4 colon cancer is classified into two categories, stage 4A and 4B:

  • 4A stage. This stage indicates that cancer has spread to one distant site, such as the liver or lungs.
  • 4B stage. This most advanced stage of colon cancer indicates cancer has spread to two or more distant sites, such as the lungs and liver.

In addition to staging, colon cancer is also classified as either low-grade or high-grade. When a pathologist examines cancer cells under a microscope, they assign a number from 1 to 4 based on how much the cells look like healthy cells.

The higher the grade, the more abnormal the cells look. Although it can vary, low-grade cancers tend to grow slower than high-grade cancer. The prognosis is also considered better for people who have low-grade colon cancer.

During the early stages of colon cancer, there are often no signs or symptoms. At later stages, symptoms tend to vary based on size and location in your large intestine. These symptoms can include:

  • change in bowel habits
  • blood in stool or rectal bleeding
  • abdominal pain
  • fatigue
  • unexplained weight loss

Doctors use a procedure called a colonoscopy to detect colon cancer. A colonoscopy is a screening test where the doctor uses a long, narrow tube with a small camera attached to view the inside of your colon.

If colon cancer is found, additional tests are often needed to determine the size of the tumor and whether it has spread beyond the colon. Diagnostic tests performed may include imaging of the abdomen, liver, and chest, such as CT scans, X-rays, or MRI scans.

There may be instances where the stage of the disease can’t be fully determined until after colon surgery has been performed. After surgery, a pathologist can examine the primary tumor, along with the removed lymph nodes, which help determine the stage of your disease.

The treatment recommended for colon cancer largely depends on the stage of the disease. Keep in mind, treatment will also take into account the grade of the cancer, your age, and your overall health. According to the American Cancer Society, typically each stage of colon cancer is treated with the following:

  • Stage 0. Surgery is often the only treatment needed for stage 0 colon cancer.
  • Stage 1. Surgery alone is recommended for stage 1 colon cancer. The technique used may vary based on the location and size of the tumor.
  • Stage 2. Surgery is recommended to remove the cancerous section of the colon and nearby lymph nodes. Chemotherapy may be recommended in certain circumstances, such as if the cancer is considered high-grade or if there are high risk features.
  • Stage 3. Treatment includes surgery to remove the tumor and lymph nodes followed by chemotherapy. In some instances, radiation therapy may also be recommended.
  • Stage 4. Treatment may include surgery, chemotherapy, and possibly radiation therapy. In some instances, targeted therapy is also prescribed.

The stage of colon cancer will affect your outlook. People diagnosed with stage 1 and 2 colon cancer generally have the highest survival rates.

Remember, the stage of colon cancer is not the only thing that determines survival rates. It’s important to understand that many factors will affect your outlook, including how well you respond to treatment, your age, your cancer grade, and your overall health at the time of diagnosis.