Colorectal cancer screening options

There’s no doubt that getting a colorectal cancer screening exam can save your life. But the idea of a colonoscopy can leave some people with the urge to put off the test, or worse, not get screened at all.

Men and women at average risk for colorectal cancer should begin regular colorectal screening exams at age 50. African American men and women should begin screening at age 45. There are alternatives to colonoscopy, but there is a lot to consider before you choose to skip this “gold-standard” test for one that may seem easier.

We talked to Selvi Thirumurthi, M.D., M.S., a gastroenterologist in the Department of Gastroenterology, Hepatology and Nutrition at MD Anderson Cancer Center, about the pros and con of several types of colorectal screening options. Here’s what she had to say.

Colonoscopy

Colonoscopy is considered the gold standard for colon cancer screening. 

During a colonoscopy, you will be sedated. Your doctor will insert a flexible tube with a tiny camera into your rectum and through the length of your large intestine (colon). Your doctor will examine the surface of your colon as she withdraws the tube.

Your colon must be completely clean in order for your doctor to see any abnormalities. The day before the test, you will prepare by avoiding solid foods and drinking only clear liquids. You also have to drink a solution that will cause you to go to the bathroom - probably several times – so there is absolutely no waste in your colon.

“Colonoscopy is the best test available to find out if a patient has colon cancer, pre-cancerous polyps, benign growths or other conditions of the colon,” says Thirumurthi. “Colonoscopy is a direct test. We’re able to completely visualize all of the lining of the colon.”

What to consider

• Prep: Colonoscopy requires you to prep your colon the day before the procedure.
• Accuracy: The colonoscopy allows your doctor to look directly at the surface of your colon. That means it’s the most accurate test for finding problems and not producing false-negative results.
• Polyp removal: A major benefit of the colonoscopy: Your doctor can remove polyps or suspicious growths during the test without scheduling another procedure.
• Risk: A colonoscopy is an invasive test. There is slight risk that your colon could be torn or punctured. Being under sedation also has risks.
• Cost: If you doctor finds polyps during the exam and removes them. That may affect what you pay.

Virtual colonoscopy

During a virtual colonoscopy, your doctor does a low-dose CT scan of your abdomen and pelvis to create 3D images. These images show polyps and other abnormalities inside your colon and rectum.

If you choose virtual colonoscopy over regular colonoscopy, MD Anderson recommends you get the test every five years starting at age 50.

What to consider

• Prep: Virtual colonoscopy requires the same prep as colonoscopy. Your colon must be completely free of waste for your doctor to perform the test. If the test detects any abnormalities, you will have to do the prep again and get a regular colonoscopy.
• Accuracy: Virtual colonoscopy is not great at detecting small polyps. What it sees as a small polyp may or may not be a polyp.
• Risk: During the test, you will be exposed to a low-dose of radiation. “It’s low-dose, but if you are getting it done regularly, then there is a cumulative effect that needs to be considered,” says Thirumurthi.
• Cost: If the test detects something, you will need to get a diagnostic colonoscopy. Since it’s not a screening exam, it likely will not be fully covered by insurance, so you will incur some cost.

Stool-based tests

Stool-based tests use a sample of your stool to look for markers – or clues – that might indicate cancer.

“All of the stool based tests are indirect tests,” says Thirumurthi. “They don’t let your doctor look at the surface of the colon, which is the best way to detect cancer and pre-cancer.”

There are several types of stool-based tests.

Stool DNA tests can detect changes in DNA that happen as colon cancer develops. Cells with the changed DNA are passed through the stool. Stool DNA tests are very good at detecting early stage cancers and precancerous polyps. This is the most accurate of stool-based tests.

FIT, or fecal immunochemical tests, test your stool for a protein found in blood. This can let your doctor know that there is blood in your stool that can’t be seen with the naked eye.

FOBT, or fecal occult blood tests, also look for blood in the stool that cannot be seen with the naked eye. It is less accurate than the FIT, and it can be tricked if the patient eats a bloody steak or takes over-the-counter medication that irritates the lining of the colon.

What to consider

• Prep: There is no prep for a stool-based test, other than some restrictions on certain foods and medicines.
• Accuracy: While some are better than others, none of the stool-based tests are as accurate as colonoscopy.
• Risk: Stool-based tests carry no risks during the test. However, you do run the risk of your doctor missing a cancer or pre-cancerous polyp, since the tests are not as accurate colonoscopy. That means there is the potential that colon cancer could go untreated for a long time, making it harder to treat successfully.
• Cost: If any of these tests come up positive, they will trigger a diagnostic colonoscopy, which will likely not be fully covered by insurance.

Get screened

No matter which exam you choose, Thirumurthi urges you to get regular colorectal cancer screenings.

Colorectal cancer is the third most common cancer for both men and women in the United States, and it’s the second leading cause of cancer-related death.

“I think the most important take home is that regardless of what type of exam people choose, that they get screened for colon cancer.”