Colorectal Cancer Screening and Prevention

‍Colorectal cancer screening prevents CRC and prevents CRC deaths.

What is cancer screening? Why is it important?

Cancer screening is looking for cancer before a person has any symptoms. Screening may lead to earlier diagnosis, earlier treatment, and better survival. When it comes to colorectal cancer, screening can prevent cancer by finding and removing polyps (abnormal growths) before they can become cancer. Almost all colorectal cancers begin as precancerous polyps in the colon or rectum. Such polyps can be present in the colon for years before invasive cancer develops, and they may not cause any symptoms. Screening can both help find cancer at an early stage and can help avoid the disease entirely.

Clinical guidelines for colorectal cancer screening vary by country. For example, the United States Preventive Services Task Force (USPSTF) recommends CRC screening for average risk adults aged 45-75. Screening may be recommended at an earlier age for patients with risk factors such as a family history of colorectal cancer or a hereditary syndrome of high risk for colorectal cancer, like Lynch syndrome or familial adenomatous polyposis. Other risk factors include age, diet, physical activity, smoking, obesity, and alcohol consumption. A personal history of inflammatory bowel disease, like Crohn's disease or ulcerative colitis, also puts you at increased risk of colorectal cancer. Always talk to your healthcare provider about when you should start getting screened and which screening method is right for you.

It is important to remember that your doctor does not necessarily think you have cancer if they suggest a screening test. Screening tests are given when you have no cancer symptoms. Screening tests may be repeated on a regular basis. If a screening test is abnormal, you may need to have more tests done to find out if you have cancer. These are called diagnostic tests.

Screening for colorectal cancer (CRC) decreases the number of deaths from the disease.  

How is colorectal cancer screening done?

Available screening options vary by country. Options may include colonoscopy, sigmoidoscopy, virtual colonoscopy, fecal immunochemical testing, guaiac fecal occult blood testing, stool DNA testing, and double-contrast barium enema testing. Talk to your doctor about your colorectal cancer risk, when you should have colorectal cancer screening, and which screening method is best for you. The timing and method of screening are based on whether you are at average risk or higher risk of CRC, availability of tests, and your personal preference.

Colonoscopy

A colonoscopy is a procedure where a long, lighted tube is inserted into the rectum and the healthcare provider examines the rectum and the entire colon. In the United States, most colonoscopies are performed while the patient is under sedation. However, the use of sedation varies around the world. Colonoscopies can find and remove precancerous growths/polyps before they come cancer. Before a colonoscopy, the patient must completely empty the bowel with a preparation procedure that may include brief diet changes, laxative (cathartic) medications, and enemas. There is a small risk from the procedure and medication. Colonoscopies are the most expensive screening choice.

Fecal Immunochemical Test (FIT or iFOBT)

The FIT or iFOBT tests for very small amounts of blood in the stool, a common symptom of colorectal cancer. The FIT (or iFOBT) involves swabbing a bowel movement and placing the swab on a card. The test may not detect blood from further up the digestive tract, such as the stomach. Testing is done at home, meaning the patient performs the sample collection and testing. The FIT test requires no colon preparation and is inexpensive. If blood is detected, a colonoscopy will be required.  

Stool DNA Test

The stool DNA test looks for abnormal DNA in the stool, which is a sign of colorectal cancer. This test is sometimes known by the brand name Cologuard. The test can detect precancerous polyps as well as cancers that do not bleed. The stool DNA test involves the patient collecting a stool sample at home and mailing it to the laboratory. There is no colon preparation involved. The stool DNA test has high detection rates of colorectal cancer.  

Guaiac Fecal Occult Blood Test (FOBT)

The FOBT tests for small amounts of blood in the stool, a common symptom of colorectal cancer. The FOBT involves swabbing a bowel movement and placing the swab on a card. Testing is done at home, meaning the patient performs the sample collection and testing. Guaiac FOBT testing requires a restricted diet and multiple days of stool collection. It is an inexpensive screening method. There is a high false-positive rate, and the FOBT may miss tumors that bleed in very small amounts or not at all. If blood is detected, a colonoscopy will be required.

Blood DNA Test

In 2024, the U.S. Food and Drug Administration approved the first blood test as a primary screening option for colorectal cancer. This test, known by the brand name Shield, detects cancer derived changes in DNA that is circulating in the blood, known as cell-free DNA. If the Shield test finds this abnormal DNA,  a colonoscopy is required for definitive diagnosis. The Shield blood test is for adults aged 45 or older who are at average risk of colorectal cancer.

Sigmoidoscopy

A sigmoidoscopy is a procedure where a long, lighted tube is inserted into the rectum and the healthcare provider examines the rectum and the sigmoid segment of the colon. The sigmoidoscopy does not require sedation and takes only 20 minutes. Not all polyps can be removed during a sigmoidoscopy, but they can be biopsied to detect colon cancer and rectal cancer. The sigmoidoscopy does not include examination of the entire colon, so some polyps or cancers could be missed. A sigmoidoscopy requires enema preparation before the procedure. Many primary care providers can do the test in their offices, and it is less expensive than a colonoscopy.  

Virtual Colonoscopy

A virtual colonoscopy can detect polyps less invasively than conventional colonoscopy and does not involve sedation of the patient. Virtual colonoscopy is less effective in the detection of flat polyps and polyps smaller than five millimeters. Preparation involves a clear, liquid diet for one to three days prior. Virtual colonoscopy uses x-rays and computers to take images. Virtual colonoscopies are expensive, but less so than a colonoscopy. If polyps or other abnormalities are found, a colonoscopy will be required.

Double-Contrast Barium Enema

A double-contrast barium enema involves pumping air and barium into the rectum. An x-ray is then performed, and the way the barium solution appears in the x-ray image will reveal abnormalities such as polyps or tumors. The double-contrast barium enema can find cancer in the earliest stage when it is most treatable. Polyps cannot be removed during the procedure. The double-contrast barium enema involves colon preparation with laxative (cathartic) medication. It is accurate for finding abnormalities and lesions in the colon and is less expensive than a colonoscopy. If polyps or other abnormalities are found, a colonoscopy will be required.  

The digital rectal exam, sometimes called a rectal exam or prostate exam, is NOT a screening test for colorectal cancer.

Talk to your doctor about your level of risk for colorectal cancer and which screening test best meets your needs.  

Colorectal Cancer Prevention

The most effective way to prevent CRC is through colon cancer screening. Colorectal cancer is somewhat unusual in that it can be prevented by diagnosing and removing colon polyps before they become cancerous. This is done by regular colorectal cancer screening, as described above.

Another part of cancer prevention is addressing lifestyle risk factors.  

The American Cancer Society suggests that the following behaviors may lower your risk of colon cancer:

• eat a healthy diet, by increasing consumption of fruits, vegetables, and whole grains and limiting consumption of red meat and processed meat
• maintain a healthy weight
• increase the amount and intensity of physical activity (exercise)
• don't drink alcohol, or reduce alcohol consumption
• don't smoke

These lifestyle changes can lower your risk of CRC as well as many other types of cancer, heart disease, and diabetes.

In addition, there is research underway to determine the role of certain medications and dietary supplements in CRC prevention.