Colon cancer screening decisions: what is the best option and when?

Colorectal cancer (CRC) is the second leading cause of cancer death in the United States, and rates are rising, especially among adults between the ages of 20 and 49. Unfortunately, approximately 30% of eligible people in the United States have still not been screened for CRC.

Colon cancer can be prevented with screening tests that look for cancer or precancerous growths called colon polyps.

When to start screening?

The United States Preventive Services Task Force recommends starting CRC screening at age 45 for average-risk patients. These guidelines reflect the most recent research on when the risk of colon cancer begins to increase.

Average-risk patients are those who have no personal or family history of colon cancer or a genetic condition that increases the risk of developing CRC. For this reason, it is important for patients to share their family history, including any cancer diagnoses in blood relatives, with their primary care physician, who can help decide the right time to start colon cancer screening. .

High-risk patients are advised to start screening before the age of 45. A primary care physician can help determine when and how a patient who is concerned about their level of risk should be screened for CRC. Patients with a history of CRC or polyps; a first-degree relative with CRC or advanced polyps (those that would have become CRC had they not been removed); a family history of certain genetic syndromes; or a history of inflammatory bowel disease (such as Crohn’s disease or ulcerative colitis) are some examples of high-risk factors.

What are the options for CRC screening?

Colonoscopy: Colonoscopy is the gold standard of screening tests and identifies approximately 95% of CRCs. It is also the only method that allows a gastroenterologist to detect and remove potentially precancerous colon polyps. Colonoscopies are considered low-risk procedures, but they have a low risk of bleeding and perforation that increases in older age groups.

Patients should cleanse their colon before the procedure by drinking a colonoscopy preparation, which removes stool from the colon so that it can be properly assessed during the procedure. Prescribing instructions for the preparation are provided by the gastroenterologist’s office.

In most cases, the procedure will be performed under sedation to ensure the patient is as comfortable as possible. It is important to note that patients are not placed under general anesthesia, but most remain drowsy and comfortable throughout their colonoscopy.

During colonoscopy, a gastroenterologist inserts a flexible tube with a camera at the end, called a colonoscope, into the rectum. The entire colon is then carefully examined. If no polyps are detected and the preparation (cleansing) of the colon is adequate, a new colonoscopy is suggested in 10 years. If polyps are detected or if the patient’s risk level or symptoms change, this interval will be shorter.

FIT test: The fecal immunochemical test (FIT) is a laboratory test that looks for hidden blood in the stool. Patients use a kit to collect their stool, then use a probe to scrape the stool, which is then placed in a tube and sent to the lab. The FIT tests are repeated every year. A disadvantage of the FIT test is that it has a false positive rate of around 5%. It can effectively exclude CRC with 79% accuracy. The FIT test is non-invasive, convenient, and cost-effective, making it an acceptable alternative to colonoscopy for many people. If a stool test is positive, a colonoscopy is needed to assess the reason for the positive test.

Flexible sigmoidoscopy: A flexible tube equipped with a camera makes it possible to observe the rectum and the lower part of the colon. The advantages of this procedure are that it is faster than a colonoscopy (only 5-15 minutes) and requires less aggressive laxative medications. Typically, patients receive flexible sigmoidoscopy every five years if no polyps are found. Because this test does not examine the entire colon, it cannot detect cancers or polyps in the unexamined part. At best, it can detect 70% of cancers and polyps.If an abnormality is found, a follow-up colonoscopy is needed to examine the entire colon.

CT colonography: A CT scan is used to view your rectum and entire colon. Just like a colonoscopy, patients should take laxative medication the night before to empty the colon. A small tube is placed in the rectum to dilate the colon to obtain clear images. This test may be useful for patients who cannot tolerate anesthesia or who have other medical conditions that prevent them from having a colonoscopy. A disadvantage of CT colonography is radiation exposure and the discovery of unrelated abnormalities outside the colon that can lead to unnecessary testing. Although CT colonography is approximately 88.7% accurate in detecting certain polyps, it is less accurate than colonoscopy as a whole. If the result of the CT colonography is abnormal, a colonoscopy is necessary for a complete evaluation of the colon.

Cologuard: This is a test where patients collect their stool, scrape it with a probe, insert it into a container with a preservative, and send it to the lab. This test looks for atypical DNA or traces of blood in the stool collected which may suggest precancerous polyps or CRC. Typically, patients repeat the test every three years. If the Cologuard test is positive, a colonoscopy is needed for further evaluation. However, the accuracy of Cologuard is still limited; 13% of the time, the test indicates that the patient may have cancer when he does not. In 2019, a study showed that the annual FIT test or colonoscopy may be more effective and less expensive than Cologuard. Further research is ongoing to assess the accuracy (and therefore usefulness) of this test for detecting CRC.

Which screening option to choose?

The most important part of colon cancer screening is getting a screening test. For most patients, colonoscopy or the FIT test are the most common ways to screen for colon cancer. However, there are other options to consider if you cannot undergo or are uncomfortable with the colonoscopy or FIT test. Ultimately, this is an important, personalized decision, and discussion that a patient should have with their health care provider, so that the right test can be done at the right time.


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