What is colorectal cancer?


Colorectal cancer is cancer that originates in the colon or rectum. Cancer happens when cells multiply too fast and don’t die when they should, which can create a mass of cells known as a tumor. In colon cancer, the large intestine, which is part of the lower bowel, develops these malignant cancer cells that form tumors in the lining of the colon. The colon is a part of the large intestine, making up a 5-foot section of the lower bowel that extracts salt and water from undigested food (stool) and pushes the stool along to the rectum. The colon has four parts:

  • Ascending colonThis is the first section of the colon and contains a pouch where the small intestine deposits any remaining undigested food. 
  • Transverse colon: This second section travels back to the other side of the body and together with the ascending colon make up what doctors refer to as the proximal colon.
  • Descending colon: This part of the colon travels downward and together with the sigmoid makes up the part of the colon doctors call the distal colon.
  • Sigmoid colon: This “s” shaped part attaches to the rectum and is the last section of the colon.

Colorectal cancer is common in both men and women after the age of 50. There are several different types of colon or rectal cancer, depending on the location and type of tumors:

  • Adenocarcinomas: Most colorectal cancer (95%) is this type in which cancer cells start in the mucus of the colon and rectum.
  • Carcinoid tumors: This type of colorectal cancer is caused by hormone-making in the colon.
  • Gastrointestinal stromal tumors (GISTS): These tumors are caused by specialized cells that attach to the walls of the colon.
  • Lymphomas: This type of immune system cancer usually begins in the lymph nodes but can sometimes start in the colon.
  • Sarcomas: This is a type of rare, soft-tissue tumor that affects blood vessels and the muscles and tissue of the colon.

When to See a Doctor

If you experience any symptoms, you should consult your doctor, who may order tests to see if you have colorectal cancer. Because it is the third most common type of cancer among men and women, yearly screenings for people over the age of 50 are highly recommended. If you have risk factors, your doctor may suggest a more frequent schedule for screening.


Because colorectal cancer has several kinds of risk factors, it can be prevented in part by addressing those lifestyle factors that are within your control. Many cancers share the same kinds of risk factors. Here are just a few to focus on to prevent colorectal and in many cases, other types of cancer.

Quit smoking

Smoking is a major factor in increased risk of cancer, not just of the lungs, but in other parts of the body.

Drink less alcohol

Excessive consumption of alcohol has been linked to a greater risk of cancer.


A healthy lifestyle that includes daily exercise can lower general cancer risk.

Healthy diet

A diet low in fat and high in fiber can reduce your risk of colorectal cancer.

Symptoms and Causes


Colorectal cancer often has few symptoms until it reaches the advanced stages, so it’s important that both men and women over the age of 50 have yearly screenings. The symptoms of colon or rectal cancer can include the following:

  • Diarrhea or constipation
  • A feeling that the bowel is still full even after passing stools
  • Blood in the stool
  • Narrow stools
  • Frequent gas or cramps
  • Weight loss
  • Fatigue
  • Nausea or vomiting

Diagnosis and Treatment


Several tests can be done to determine if you have colorectal cancer. They might include some or all of these:

  • Digital rectal exam
  • Colonoscopy
  • Fecal occult blood test
  • Blood test
  • Barium enema or x-rays of the intestine
  • Biopsy

Your doctor might order other tests not listed here to help diagnose this kind of cancer.
Your doctor’s diagnosis will usually include which stage of cancer you have. A stage is defined as not only how far the cancer has spread, but to what parts of the body. The stages of colorectal cancer are generally defined here, but there are sub-stages and specifics with each stage that you should discuss in depth with your doctor.

  • Stage 0: This is the earliest stage of cancer where the cells have not grown beyond the inner layer of the intestine.
  • Stage 1: This stage describes growth into the wall of the intestine but has not spread to any lymph nodes or other areas.
  • Stage 2: The outermost layers of the colon are affected by cancer at this stage, but other organs and lymph nodes are not.
  • Stage 3: Tumors have penetrated through the layers of the colon but not reached other organs. Some surrounding lymph nodes are usually affected at this stage. 
  • Stage 4: Tumors have penetrated the colon and cancerous cells have spread to other organs of the body, with or without affecting lymph nodes. The most common organs to be affected at this point are the liver and the lungs. This stage is often referred to as metastasized cancer.

For a more detailed explanation of the stages and sub-stages of colorectal cancer, consult your doctor or oncologist.