What Is Colorectal Cancer?

Colorectal cancer (CRC) is a type of cancer that can affect the colon and the rectum, which together make up our large intestine (also known as the large bowel). They are a part of our digestive system. 

Detailed information on how the digestive system functions can be found here

The colon is composed of four sections:

  • The first section is the ascending colon, which receives undigested food from the small intestine and travels upward through the abdominal cavity. 
  • The second section is called the transverse colon because it goes across the body. 
  • The third part of the colon is called the descending colon because it travels downwards. 
  • The last section of the colon is connected to the rectum and is called the sigmoid colon

The rectum receives waste matter from the colon and stores it before it exits the body through the anus.

What Is a Polyp, and Does It Cause CRC?

A polyp is a group of cells that can grow inside the colon and potentially become cancerous. Polyps can be:

  • Pedunculated, which hang from a stalk
  • Sessile, which are flat

Some types of polyps, like hyperplastic polyps, which grow near the end of the colon, remain benign, meaning they are not cancerous. The adenomatous polyps, however, can become cancerous over time, (also called pre-cancerous). Sessile serrated polyps and traditional serrated adenomas have a higher risk of developing into CRC.

If a polyp is larger than 1cm or if multiple polyps are present, it may suggest that a person is at a high risk of developing CRC. If a polyp becomes cancerous, it can grow into the wall of the colon or rectum and eventually grow into the blood vessels or lymph vessels. This is how the cancer can spread to other organs in the body (metastasis). 

Additional information on polyps and their risks can be found here.

Who Is at a High Risk of Developing CRC?

 

The risk of CRC increases with age, and it is most commonly seen in adults over the age of 50 years. Men and women are equally likely to get colon cancer, but men have a higher risk of developing rectal cancer than women. A family history of colorectal cancer, inflammatory bowel disease (including ulcerative colitis or Crohn’s disease) may also increase a person’s risk of developing CRC. Also, a personal history of inflammatory bowel disease, colorectal polyps, or CRC can put you at high risk for CRC. Race is also a risk factor: African Americans have >20% higher incidence rate of CRC than white people. 

You can read more about risk factors and screening here.

Stages of CRC

CRC staging is based on how far the cancer has spread. This information is used by your doctor to decide the course of treatment. Treatment-related information can be found here.

  • Stage 0: This is the earliest stage of CRC in which the cancer has not grown past the inner layer of the colon or rectum 
  • Stage 1: The cancer has not spread to the lymph nodes but has grown past the inner layer of the colon or rectum (T1 or T2, N0, M0)
  • Stage 2: This is sub-classified as:
    • Stage 2A: The cancer has not spread to the lymph nodes, but has grown through the wall of the colon or rectum (T3, N0, M0)
    • Stage 2B: The cancer has not spread to the lymph nodes or elsewhere, but it has grown through the layers of the muscle to the lining of the abdomen (T4a, N0, M0)
    • Stage 2C: The cancer has not spread to the lymph nodes or elsewhere, but it has spread through the wall of the colon or rectum and has grown into the structures nearby (T4b, N0, M0)
  • Stage 3: This is sub-classified as:
    • Stage 3A: The cancer has invaded the lining of the intestine and spread to 1-3 lymph nodes or to a nodule of tumor cells in tissues around the colon or rectum, but not to other parts of the body. (T1 or T2, N1 or N1c, M0; or T1, N2a, M0).
    • Stage 3B: The cancer is still ‘localized’ and has grown through the intestinal wall into the surrounding organs and into 1 to 3 lymph nodes, but not to other parts of the body (T3 or T4a, N1 or N1c, M0; T2 or T3, N2a, M0; or T1or t2, N2b, M0)
    • Stage 3C: The cancer has spread to 4 or more lymph nodes but not to other distant parts of the body (T4a, N2a, M0; T3 or T4a, N2b, M0; or T4b, N1 or N2, M0)
  • Stage 4: This is sub-classified as:
    • Stage 4A: The cancer has spread (metastasis) to a single other organ such as lungs or liver (any T, any N, M1a)
    • Stage 4B: The cancer has spread to more than 1 other organ (any T, any N, M1b)
    • Stage 4C: The cancer has spread to the peritoneum, which is the tissue that lines the abdomen. It may have also spread to other organs or sites. (any T, any N, M1c)
  • Recurrent: Cancer that has returned following prior treatment. 

More about T, N, and M.