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Colorectal Cancer Screening

Cross section of sigmoid colon, rectum, and anus showing cancer and polyp.Colorectal cancer is cancer in the colon or rectum. It is a leading cause of cancer deaths in the U.S. But when this cancer is found and removed early, the chances of a full recovery are very good. Because colorectal cancer rarely causes symptoms in its early stages, screening for the disease is important. It’s even more crucial if you have risk factors for the disease. Learn more about colorectal cancer and its risk factors. Then talk to your healthcare provider about being screened.

Risk factors for colorectal cancer

Your risk of having colorectal cancer increases if you:

  • Are 50 years of age or older

  • Have a family history or personal history of colorectal cancer or polyps

  • Have a personal history of type 2 diabetes, Crohn’s disease, or ulcerative colitis

  • Have an inherited genetic syndrome like Lynch syndrome (HNPCC) or familial adenomatous polyposis (FAP)

  • Are very overweight

  • Are not physically active

  • Smoke

  • Drink a lot of alcohol

  • Eat a lot of red or processed meat

The colon and rectum

Waste from food you eat enters the colon from the small intestine. As it travels through the colon, the waste (stool) loses water and becomes more solid. Intestinal muscles push it toward the sigmoid colon. This is the last section of the colon. Stool then moves into the rectum, where it’s stored until it’s ready to leave the body during a bowel movement.

How colorectal cancer starts

Polyps are growths that form on the inner lining of the colon or rectum. Most are benign, which means they aren’t cancer. But over time, some polyps can become cancer (malignant). This happens when cells in these polyps begin growing abnormally. In time, malignant cells invade more of the colon and rectum. The cancer may also spread to nearby organs or lymph nodes or to other parts of the body. Finding and removing polyps can help prevent cancer from forming.

Your screening

Screening means looking for a health problem before you have symptoms. During screening for colorectal cancer, your healthcare provider will ask about your health history, examine you, and do 1 or more tests. To start, you may have:

  • Health history questions to answer. Your healthcare provider will ask about your health history. Mention if a family member has had colon cancer or polyps. Also mention any health problems you have had in the past.

  • Digital rectal exam (DRE). During a DRE, the healthcare provider inserts a lubricated gloved finger into the rectum. The test is painless and takes less than a minute. This test alone is not enough to screen for colorectal cancer. You will also need one of the below tests.

Screening test choices

Fecal occult blood test (FOBT) or fecal immunochemical test (FIT)

These tests check for blood in stool that you can’t see (hidden or occult blood). Hidden blood may be a sign of colon polyps or cancer. A small sample of stool is tested for blood in a laboratory. Most often, you collect this sample at home using a kit your healthcare provider gives you. Follow the instructions carefully for using this kit. You might need to not eat certain foods and not take certain medicines before the test, as directed.

Stool DNA test

This test looks for DNA changes in cells in the stool. These DNA changes might be signs of cancer. It also looks for hidden blood in stool. For this test, you collect an entire bowel movement. This is done using a special container put in the toilet. The sample is then sent to a lab for testing.

Barium enema with contrast (double-contrast barium enema)

This test uses X-rays to create images of the entire colon and rectum. The day before this test, you will need to do a bowel prep to clean out the colon and rectum. A bowel prep is a liquid diet plus strong laxatives or enemas. You will be awake for the test, but you may be given medicine to help you relax. At the start of the test, a healthcare provider who specializes in imaging tests (radiologist) places a soft tube into the rectum. The tube is used to fill the colon with a contrast liquid (barium) and air. This can be uncomfortable for some people. The liquid helps the colon show up clearly on the X-rays. Because the test uses X-rays, it exposes you to a small amount of radiation.

Virtual colonoscopy

This exam is also called a CT colonography. It uses a series of X-ray photographs to create a 3-D view of the colon and rectum. The day before the test, you will need to do a bowel prep to clean out your colon. Your healthcare provider will give you instructions on how to do this. During the procedure, you will lie on a table that is part of a special X-ray machine called a CT scanner. A small tube will be placed into your rectum to fill the colon and rectum with air. This can be uncomfortable for some people. Then, the table will move into the machine and pictures will be taken of your colon and rectum. A computer will combine these photos to create a 3-D picture. Because the test uses X-rays, it exposes you to a small amount of radiation.

Scope exams

Here are 2 types of scope exams:

  • Colonoscopy. This test can be used to find and remove polyps anywhere in the colon or rectum. The day before the test, you will do a bowel prep. This is a liquid diet plus a strong laxative solution or an enema. The bowel prep will cleanse your colon. You will be given instructions for this. Just before the test, you are given a medicine to make you sleepy. Then, a long, flexible, lighted tube called a colonoscope is gently inserted into the rectum and guided through the entire colon. Images of the colon are viewed on a video screen. Any polyps that are found are removed and sent to a lab for testing. If a polyp can’t be removed, a sample of tissue is taken and the polyp might be removed later during surgery. You will need to bring someone with you to drive you home after this test. Colonoscopy is the only screening test that lets your healthcare provider see the entire colon and rectum. This test also lets your healthcare provider remove any pieces of tissue that need to be looked at by a lab. If something suspicious is found using any other tests, you will likely need a colonoscopy.

  • Sigmoidoscopy. This test is similar to colonoscopy, but focuses only on the sigmoid colon and rectum. As with colonoscopy, bowel prep must be done the day before this test. It might not need to be as complete as the bowel prep for a colonoscopy. You are awake during the procedure, but you may be given medicine to help you relax. During the test, the healthcare provider guides a thin, flexible, lighted tube called a sigmoidoscope through your rectum and lower colon. The images are displayed on a video screen. Polyps are removed, if possible, and sent to a lab for testing.


When to call your healthcare provider after a test

Call your healthcare provider if you have any of the following after any screening test:

  • Bleeding

  • Fever of 100.4°F (38°C) or higher, or as directed by your healthcare provider

  • Abdominal pain

  • Vomiting

Online Medical Reviewer: Alteri, Rick, MD
Online Medical Reviewer: Gersten, Todd, MD
Date Last Reviewed: 12/1/2017
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