What is colon cancer?


Colon cancer, or colorectal cancer, is cancer of the colon or rectum. These structures are located at the end of the digestive system. The colon is where stool is formed before it goes through the rectum and out of the body.

Colon cancer often starts as a growth called a polyp. Polyps grow on the wall of the colon or rectum. Some polyps eventually become cancer. The best way to prevent colon cancer is find and remove polyps early.

Colon cancer is a common cancer, but the number of colon cancers diagnosed each year is going down. This is likely because more people are getting a colonoscopy and other tests for colon cancer. With a colonoscopy, the doctor can see inside the colon and find and remove any polyps.

When to See a Doctor

See a doctor if you notice any bleeding from the rectum or blood in your stool. You should also see a doctor if you have any new bowel problems or pain that does not go away within a few days.


You can lower your risk of colon cancer by doing the following:

Get Screened

Stay Active

Maintain a Healthy Weight

Limit Alcohol

Don't Smoke

Symptoms and Causes


Colon cancer may not have symptoms at first, so it is important to follow the recommendations for getting tested.

Symptoms of colon cancer include:

  • A change in your bowel movements, like constipation or diarrhea, that lasts more than a few days
  • Bright red blood from the rectum
  • Blood in the stool (can make the stool look dark or black)
  • Pressure that feels like you need to have a bowel movement, even if you just had one
  • Weight loss that is not planned

Diagnosis and Treatment


Many colon cancers are preventable if pre-cancerous polyps are removed. Polyps often take from 10 to 15 years to become cancerous. Usually these growths start before you have any symptoms. It is important to get screened for colon cancer to find and remove them.

People who have an average risk of colon cancer should start getting screened at age 50. If you have any of the risk factors for colon cancer, talk to your doctor about when to start getting screened.

These tests are used to screen for colon cancer:

  • Colonoscopy: A colonoscopy allows the doctor to see inside the rectum and colon. A very thin tube (colonoscope) with a light and lens is inserted into the rectum and colon. The doctor may remove a polyp during the colonoscopy or take a tissue sample to look at in a lab.
  • Virtual colonoscopy: This test uses CT scans (X-rays) to get images of the colon. Researchers are still testing to see if this works as well as a regular colonoscopy.
  • Sigmoidoscopy: This test is like a colonoscopy except the instrument (sigmoidoscope) only goes to the lower part of the colon (the sigmoid colon).
  • Fecal occult blood test: This test checks the stool for blood that can’t be seen by the naked eye. The lab tests a small sample of stool.
  • DNA stool test: This test checks the stool for DNA mutations that could lead to colon cancer.