Colorectal Cancer Screening

What is colorectal cancer?

Colorectal cancer (CRC) happens when an adenomatous polyp (a pre-cancer growth) forms from the normal tissue lining your colon. This process can take 10 to 15 years or longer. Many people have no symptoms of this polyp or growth. If there are symptoms, you may have bleeding, weight loss, or a change in your bowel habits.

How often is colorectal cancer found?

There are about 150,000 new cases of colorectal cancer diagnosed in the United States each year. The risk of colon cancer is much higher if you have a family history of colorectal cancer, especially in cases of familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC).

Your chance of having a polyp or cancer goes up as you get older, especially if you are in your 50s to 80s. It is important that polyp(s) are found before they become cancerous and/or to find cancer as early as possible.

How are pre-cancerous polyps or early cancers found?

Pre-cancerous polyps or early cancers are found with screening tests. There are a few tests that screen for colorectal cancers. The test you have is based on:

• Your preference.
• If the test is available.
• Cost.

Talk with your provider about when you should start having routine screenings done and what test would be best for you.

The American Cancer Society (ACS), the US Multi-Society Task Force on Colorectal Cancer (USMSTF), and the American College of Radiology have made guidelines for screening. Below are the tests that are available, how they are done, and how well they work.

Screening with Stool Testing

Stool-based tests check for blood in your stool. Some tests can also check for abnormal DNA or RNA in the cancer or pre-cancer polyps. These tests are best at detecting cancer or more advanced, larger polyps (polyps that are likely to turn into cancer). Below are the types of stool testing:

Fecal Occult Blood Testing (FOBT)

The least expensive colorectal cancer (CRC) screening test is the fecal occult blood test (FOBT). Occult means hidden or not seen by the eye. These tests take a sample of stool and use a chemical solution to check for blood in your stool. There are a few things you need to do to prepare for this test. To lower your chance of having a false-positive result (comes back positive but is really a negative result):

• Do not take aspirin or NSAID products (ibuprofen, Naprosyn) for 7 days before the testing.
• For 3 days before testing, avoid vitamin C, iron, eating red meat, and some raw vegetables/fruits (including broccoli, beets, and bananas).
• The test must be done on two or three bowel movements that are consecutive (one after the other).

For it to be most useful, this test should be done every year. If the test is positive, you will then have a colonoscopy to find and treat the cause of the positive test. The stool blood test results can vary based on the brand of test. Results can also be affected by the procedure used to process the test.

Fecal Immunochemical Test (FIT)

Fecal immunochemical test (FIT) checks for hidden blood in your stool from your lower intestines. This test is not affected by diet. FIT costs more than FOBT, and it is not clear yet if it is better. While it seems that 2 FIT test results are better than 1, the perfect number of tests per year is not yet known. FIT uses an at-home testing kit that your provider can order for you.

FIT and FOBT testing are certainly better than no screening at all. The concern is that advanced adenomas or early cancers are not likely to bleed all the time, so they may not be found by these tests. You may have a negative test even though there is cancer in your colon. The tests must be done more than once and repeated each year to have the best chance of finding cancer. These tests are less effective in finding tumors on the right side of your colon than on the left.

Multi-targeted Stool DNA and RNA Testing

Stool DNA Testing (mt-sDNA) and Stool RNA Testing (mt-sRNA) are multi-targeted (mt) tests. This means they can test for different DNA and RNA changes and look for blood in your stool.  Cancer cells or adenomas (pre-cancers) have abnormal DNA or RNA, which is shed from the lining of your bowel and passed in your stool. Since each cancer can have different DNA and RNA changes, the test looks for a few abnormalities but does not detect all the possible changes found in different people. Some tumors may not be detected. While the stool blood detection tests use a small sample of stool,  the whole stool specimen is needed for these DNA and RNA tests. mt-sDNA and mt-sRNA can be tested using an at-home testing kit that your provider can order for you.

It is possible to have a false-positive result, and no cancer will be found on further testing. Multi-targeted tests are considered highly sensitive when detecting cancer and moderately sensitive when detecting pre-cancer polyps. These tests are also less sensitive in detecting tumors on the right side of the colon than on the left. As with FOBT, if you have a positive mt-sDNA or mt-sRNA test, you will need to have a colonoscopy done.

Screening with Endoscopy

Endoscopy uses a camera on the end of a thin, flexible tube to view your bowel and look for any polyps or tumors. There are two types of endoscopy used for colorectal cancer screening: sigmoidoscopy and colonoscopy.

Sigmoidoscopy

Sigmoidoscopy uses a sigmoidoscope, a thin, flexible tube that can view about 1/3 of the colon (the left side). If a polyp or tumor is found with this test, you may need a biopsy with sigmoidoscopy, or you might need a colonoscopy and biopsy. If an adenomatous polyp is found during flexible sigmoidoscopy, then you should have a colonoscopy because there is a higher risk of an adenoma on the right side of your colon. Future screening tests should then be done with a colonoscopy.

For flexible sigmoidoscopy:

• There is less bowel prep than colonoscopy (2 enemas).
• You do not need to be sedated (made sleepy and unaware), so it may be done in a provider’s office.
• You will not need recovery time.

This test is only as good as the person performing it (their training and if they follow guidelines for the test) and how well you are prepared (a poorly done bowel prep will limit the sensitivity of the test). Although rare, the main risk of sigmoidoscopy is perforation of the bowel (injury/harm to the bowel wall), which can happen with or without a biopsy.

When used for CRC screening, the ACS and USMSTF recommend sigmoidoscopy be performed every 5 years.

Colonoscopy

The colonoscope is like the sigmoidoscope, but it is longer and can see the whole colon (left and right sides). If a polyp is found, it can be removed using a cutting tool and sent to a pathology lab to see if it is adenomatous (precancerous). Colonoscopy is thought to be the gold standard of CRC screening, but it is only as good as the provider (called an endoscopist) doing the test. Given the slow growth of polyps, a colonoscopy (in the general population) should be done every 10 years. Those at higher risk (such as those with family history, prior test with polyps, personal history of ulcerative colitis (UC), HNPCC, or FAP) should be screened more often. Talk with your provider about how often you should have this test.

To prepare for a colonoscopy, you must clean out your bowel. To do this, you must follow a low-fiber, clear liquid diet for 1 to 2 days before. You also need to do a bowel cleansing or prep, which is done with laxative solutions or tablets you take by mouth. Your provider will give you instructions.

During the test, your bowel is filled with air, so the endoscopist can look at your colon. You will likely need to be sedated, so you will need someone to pick you up and take you home after the procedure. You will likely need to take the day off from work. The main risks of colonoscopy are bleeding after the removal of a polyp and perforation of your bowel.

Colonoscopy Follow-Up

You are at an increased risk for future findings of cancer or pre-cancer if you have either:

• 3 or more adenomas.
• High-grade dysplasia.
• Villous features (growths that are likely to turn into polyps).
• An adenoma 1 centimeter (cm) or larger in size.

If you are at an increased risk, it is recommended by the USMSTF that you have a 3-year follow-up colonoscopy and one every 3 years. If you are at lower risk, you can have a follow-up in 5 to 10 years. If you have hyperplastic polyps and are considered average-risk, you should have a 10-year follow-up. More frequent screening is recommended if you have a suspected or proven genetic syndrome (HNPCC and FAP). It is unclear how a family history without a genetic syndrome should affect screening guidelines and timing.

Additional Screening Tests

Blood-based Testing

If you choose not to have stool or any other type of testing, blood-based testing is an option. Your blood will be drawn in your healthcare provider’s office to check for tumor DNA in your blood. Blood-based testing is less sensitive in detecting adenomatous polyps (pre-cancers) and stage I (one) colon cancer. If you have a positive result, you will need to have a colonoscopy done.

Virtual Colonoscopy

Virtual colonoscopy (VC) is a way of looking at the colon from outside the body, using a CT scan. For the procedure, you will lie on a table that passes through a donut-like machine that takes pictures from different angles around your body. The 2-dimensional (2D) images of your colon are turned into three-dimensional (3D) images and looked at by a trained radiologist or gastroenterologist.

 You will only be in the scanner for about 10 minutes, but the whole test takes about 30 minutes. The 30 minutes includes reading and interpretation, which does add to the cost of the procedure. For these images to be accurate, you must do bowel prep similar to a colonoscopy (dietary changes and oral laxatives). However, for the virtual scan, the bowel may need to be a bit clearer. This is because during a normal colonoscopy, the provider can clear away any stool that is left behind, but they cannot do this with VC. You will also have a drink called a contrast medium the night before your test. This helps the provider see the difference between stool that is leftover in your colon and polyps.

A tube is put into your rectum, and air or carbon dioxide is pumped into your colon. This happens just before the CT to expand your colon so that it can be more clearly seen. In some centers, you will be given an IV (intravenous) medication called glucagon. Glucagon helps your bowel walls relax and can improve the view of your bowels, but it is now less commonly used. There is no sedation, so you will not need any recovery time, but some say they feel more discomfort than with a normal colonoscopy.

VC is better at detecting cancers and larger polyps than smaller polyps or flat lesions (also called non-polypoid lesions). Some providers have suggested that smaller polyps are less likely to turn into cancer, so the decreased ability to detect them may not be significant.

As with most CRC screening tests, it is only as good as the provider doing the test. Many of the studies were done with the best equipment and well-trained radiologists, which may overestimate how good the test is. If polyps are detected, you may be referred for a normal colonoscopy for polyp removal and biopsy.

There is a very small risk of bowel perforation while air is pumped into your bowel. There is concern among some experts about the lifetime dose of radiation received during this and other radiology exams, but this risk is not yet well understood. Because the test is a CT scan and includes other areas of your abdomen, there may be findings outside of your colon that may need more workup. As a screening method, if you are average-risk, VC should begin at age 50. How often you should have this test has not been studied, but it is recommended that the test be done every 5 years.

Double Contrast Barium Enema

A double-contrast barium enema (DCBE) is done by placing a small tube into your rectum and coating the inside of your colon with barium (a contrast agent) and pumping in air to distend (stretch) your colon. X-rays are taken in different positions to look at the colon lining. You will need to do bowel prep, similar to that used with traditional colonoscopy, with diet changes and oral laxatives. No sedation is used for the procedure. You may have discomfort during or after the test, which takes 20 to 40 minutes. The test looks at your whole colon and can often detect most cancers and significant polyps, though formal clinical studies have not been done. The test may be a good option if you cannot have a colonoscopy  (due to a blockage or contraindication).

If a polyp greater than 5 millimeters (mm) is found, you will need to have a colonoscopy to biopsy this finding. As with many CRC screening tests, the test is only as good as the provider doing and reading the test and your bowel prep before the test. Because your colon is being looked at from the outside, leftover stool in your bowel can be mistaken for polyps or can hide other findings. The test is safe, though bowel perforation remains a low risk. The use of the DCBE has decreased over the past 10 years, with the test being largely replaced with colonoscopy. When used for colorectal cancer screening, DCBE should be done every 5 years in average-risk adults over 50 years of age.

Screening Guidelines

There are guidelines for CRC screening by the ACS and the USPSTF (US Preventive Services Task Force). If you are at average risk, you should start screening at age 45 according to the ACS and the USPSTF. Keep in mind that the best screening test is one that is actually done. You should talk with your provider about your options and their recommendations based on your risk factors, preference, and insurance coverage/cost.

• Flexible sigmoidoscopy: Every 5 years.
• Colonoscopy: Every 10 years.
• Double-contrast barium enema: Every 5 years.
• CT colonography (virtual colonoscopy): Every 5 years.
• Fecal occult blood test (FOBT): Every year.
• Fecal immunochemical test (FIT): Every year.
• Multi-targeted stool DNA test (mt-sDNA): Every 3 years.
• Multi-targeted stool RNA test (mt-sRNA): Every 3 years.

If your baseline screening detects polyps or cancer, you will need to plan with your provider how often you should be tested and which test is best. You should talk about your risk with your provider, but the following factors increase risk and therefore increase the screening recommendations:

• A history of an adenomatous polyp or colorectal cancer.
• If you have inflammatory bowel disease (Crohn’s disease or ulcerative colitis).
• If a family member has had colorectal cancer or adenomatous polyps, and if so, how many polyps and at what age. Also, whether they are a first-degree relative (parent, sibling, child) is important to your risk. Screening often will begin 10 years before the age of your relative’s diagnosis.
• If the family has a known or suspected genetic syndrome (HNPCC or FAP).

The best way to prevent colon cancer is through screening. It is important to work with your care providers to determine what test will work best for you, how your health insurance covers it, and what to do if abnormalities are detected.

To learn about factors that could affect your cancer risk, use the Reduce My Risk tool.