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Quick Facts

Colon Cancer

(Colorectal Cancer)


The Manual's Editorial Staff

Last full review/revision Mar 2021| Content last modified Mar 2021
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Your colon is your large intestine. Your rectum is a pouch at the end of your colon where stool is stored until you pass it.  

Locating the Large Intestine

Locating the Large Intestine

What is colon cancer?

Cancer is the out-of-control growth of cells in your body. Cells are the tiny building blocks of your body. Cells specialize in what they do. Different organs are made of different kinds of cells. Almost any kind of cell can become cancerous.

Colon cancer is cancer that starts in the lining of your colon. Rectal cancer is very similar. The two cancers are sometimes referred to as colorectal cancer.

  • The most common symptoms are bleeding when you pass stool and feeling tired and weak

  • Everyone over the age of 45 should be screened for colorectal cancer

  • Colon cancer caught early is more curable

  • Doctors usually remove the cancer with surgery

What causes colon cancer?

Colorectal cancer is caused by the out-of-control growth of cells in the lining of your colon or rectum. You're more likely to get colorectal cancer if you:

  • Have polyps (abnormal growths) in your colon

  • Have a colon disease, such as ulcerative colitis or Crohn disease

  • Eat a lot of fat, meat, and processed foods and not much fiber

  • Have family members who have had colorectal cancer or colon polyps

What are the symptoms of colon cancer?

Colon cancer grows slowly and doesn't cause symptoms for a long time. Symptoms may include:

  • Feeling weak and tired—in some people this is the only symptom

  • Belly pain

  • Constipation (trouble passing stool)

  • Blood in your stool

  • Feeling like your rectum isn’t completely empty after passing stool

Sometimes the cancer blocks your colon, and you get symptoms of a bowel obstruction, such as throwing up, or having crampy belly pain or a swollen belly.

How can doctors tell if I have colon cancer?

If you have symptoms that doctors think might be from colon cancer, they usually do: 

If colonoscopy shows cancer, then doctors usually do:

How do doctors screen for colon cancer?

Because colon cancer is so common, doctors recommend screening tests to look for cancer before it causes symptoms. Screening for colon cancer usually begins at age 45 but earlier if you have certain high risk factors. Talk to your doctor about when you need to start screening.

Screening tests include:

  • Testing your stool for blood you can't see

  • Sigmoidoscopy (doctors use a flexible viewing tube inserted through your anus to look at the lower part of your large intestine)

  • Colonoscopy (to have a more complete view of the intestine than is possible with sigmoidoscopy, doctors thread a thin, lighted tube with a small camera through your anus to look at all of your colon)

  • CT colonography (CT scan to look at your colon after you drink a special fluid and have your colon filled with air, which helps with the imaging)

How do doctors treat colon cancer?

Doctors treat colon cancer with:

  • Surgery to take out the cancerous part of your colon and join the two cut ends together

  • Sometimes, chemotherapy after surgery

Understanding Colostomy

In a colostomy, the large intestine (colon) is cut. The part that remains connected to the colon is brought to the skin surface through an opening that has been formed. The part is then stitched to the skin. Stool passes through the opening and into a disposable bag.

Understanding Colostomy

For rectal cancer, doctors do:

If doctors have to take out your rectum, you usually will need a colostomy. With a colostomy, doctors attach the end of your colon to an opening in the wall of your belly. Your stool comes out of this opening into a plastic colostomy bag. The bag is stuck onto your belly with adhesive and you change it when it fills up.

After your treatment, doctors will continue to care for you and check on your health with regular testing, such as:

  • Colonoscopy

  • Blood test

  • Liver tests

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