Colon cancer is a type of cancer that affects the colon, i.e. the last part of the large intestine. When a person is diagnosed with this disease, one of the first things that every doctor will do is determine its stage. Knowing this will help to conclude the extent to which cancer has spread. Staging is also one of the deciding factors for which method of treatment is used to cure various types of cancer, including colon cancer.

The main stages of colon cancer are generally decided on the basis of the TNM staging system. This staging system takes the following factors into consideration:

• Primary tumor (T): This refers to how big the original tumor mass is and whether it has invaded the nearby areas or not.
• Regional lymph nodes (N): This helps to determine whether or not cancer has spread to the nearby lymph nodes.
• Distant metastases (M): This determines whether cancer has spread to other body parts, such as the liver or the lungs.

The main stages of colon cancer
The main stages of colon cancer are as follows:

Stage 0
This is the first form of cancer. Stage 0 implies that the tumor has not spread beyond the innermost layer of the colon, i.e. the mucosa.

Stage 1
This stage indicates that the tumor has invaded the mucosa and even the next layer of the colon, which is known as submucosa. However, it has not yet spread to the lymph nodes.

Stage 2
When colon cancer reaches stage 2, it is considered to be slightly more advanced. This stage indicates that the tumor has invaded beyond the mucosa and submucosa layers. Stage 2 is further classified into three stages, namely 2A, 2B or 2C.

• 2A: This specifies that the tumor has not reached the nearby tissues or lymphatic nodes. However, it has reached the outermost layers of the colon.
• 2B: This indicates that the tumor has grown through the outer layer of the colon as well as the visceral peritoneum, i.e. the membrane that keeps the abdominal glands in place, but it has not spread to the lymph nodes.
• 2C: Cancer has not reached the lymph nodes but has affected the nearby organs.

Stage 3
Stage 3 is further classified into three stages, namely 3A, 3B or 3C.

• 3A: This indicates that the tumor has reached the nearby lymph nodes.
• 3B: This indicates that the tumor has affected one to three lymph nodes and has also invaded nearby organs and structures.
• 3C: This indicates that the tumor has extended beyond muscular layers and has affected more than four lymph nodes. It has also invaded nearby organs and structures.

Stage 4
This is the last stage of colon cancer which is categorized into two stages, namely 4A and 4B.

• 4A: This stage implies that colon cancer has affected one of the distant organs such as the liver or the lungs.
• 4B: This is the most advanced stage that indicates that the tumor has spread to two or more distant organs.