FDA Approves Blood Test for Colon Cancer Screening — What This Means for Patients

A New Tool in Colon Cancer Detection

• In recent years, there has been a concerning rise in colon cancer rates among people younger than 55, with rates increasing by 1-2% annually.
• A blood test called Shield is now FDA-approved for colon cancer detection.
• Initially available for $895 out-of-pocket, the approval means the test is now more likely to be covered by Medicare and private insurance, making it more accessible.
• Research shows Shield is 83% effective in finding colorectal cancers by detecting DNA traces left by cancer in the bloodstream.
• The test is recommended to be given every three years, starting at age 45.
• It’s important to say that Shield does not replace colonoscopies — but serves as an early warning sign, prompting follow-up with medical professionals for more definitive testing.

The US Food and Drug Administration (FDA) has approved a new screening blood test for detecting colon cancer. This approval could significantly boost screening rates for colon cancer, which has been diagnosed in younger adults more frequently in recent years. Colon cancer is the second-most common cause of cancer-related deaths in the United States. Early detection and regular screening can dramatically improve outcomes and save lives. The new blood test, called Shield, was developed by Guardant Health and could be a helpful tool in the fight against colon cancer. However, experts warn that it should not replace colonoscopies. "This is definitely not practice changing, although it does offer opportunity for people who might otherwise not get colonoscopy and maybe it would be more affordable," Dr. Heather Yeo , assistant attending surgeon at NewYork-Presbyterian/Weill Cornell Medical Center, told SurvivorNet. A screening test is used to look for a disease when a person doesn't have symptoms (when a person has symptoms, diagnostic tests are used to find out the cause of the symptoms).

How Does Shield Work?

"This test works by looking for cancer DNA in the blood. Unfortunately, there are false negatives, and also false positives, and it does not pick up the majority of polyps or pre-cancer," Dr. Yeo explains. The Shield test detects colorectal cancers by identifying DNA fragments that cancerous tumors release into the bloodstream. Research published found that Shield is 83% effective at detecting colorectal cancers. However, it is less effective at finding precancerous growths, detecting only 13% of earlier-stage polyps. Colonoscopies, on the other hand, can detect these polyps. Despite this limitation, the test's ability to find later-stage cancers can significantly impact patient outcomes. One of Shield's most significant advantages is its simplicity. A blood sample can be collected during a routine doctor's visit or at a commercial lab, without the need for fasting or bowel preparation required for a colonoscopy. Dr. Heather Yeo clears up some common myths about colon cancer. "The only thing this might be helpful for a screening adults who are high-risk for colonoscopy, or those who refuse to get colonoscopy. Otherwise colonoscopy remains the standard of care," says Dr. Yeo. This ease of testing could encourage more people to undergo screening, particularly those in their 40s and 50s who may be less likely to comply with traditional screening methods due to busy schedules and other responsibilities.

The Importance of Screening

"If this test is positive, a patient will need a colonoscopy. If this test is negative it is also recommended that a patient might get a colonoscopy, because this test does not pick up early tumors/polyps. Colonoscopy is the gold standard because it picks up polyps, which are pre-cancer, and prevents them from turning into cancer. This test is not very good at picking up polyps," adds Dr. Yeo. Regular screening is crucial because colorectal cancer is often preventable through early detection and removal of precancerous polyps. Colonoscopy remains the gold standard for detecting and preventing colorectal cancer, with a 95% detection rate for large polyps. However, screening rates are low, with fewer than 60% of eligible people having their recommended screening. The inconvenience and discomfort associated with colonoscopies and fecal tests contribute to these low rates. While Shield doesn't replace colonoscopies, it can serve as an early warning sign, prompting patients to seek further testing from medical professionals.

What is a Colonoscopy?

A colonoscopy is a medical procedure used to examine the inside of the colon (large intestine) and rectum. It is performed by a gastroenterologist, who uses a long, flexible tube called a colonoscope to view the lining of the colon. The colonoscope has a camera and a light at its tip, allowing the doctor to visualize the colon and identify any abnormalities, such as polyps, ulcers, or signs of cancer. During a colonoscopy, the patient is typically given sedation to help them relax and minimize discomfort. The colonoscope is gently inserted through the anus and advanced through the colon while the doctor carefully examines the colon lining. If any abnormal tissue or polyps are found, they may be removed or biopsied for further examination.

What About Insurance Coverage?

With the FDA's approval, Shield is now likely to be covered by Medicare and private insurance companies, making it more accessible to a broader population. Previously available for around $900 out of pocket, the test's cost may now be significantly reduced for patients, removing a financial barrier to screening.

Who Should Undergo Colon Cancer Screening?

The Centers for Disease Control and Prevention (CDC) and the U.S. Preventive Services Task Force recommend that adults age 45 to 75 be screened for colorectal cancer. This new test needs to be administered at least every three years, starting at age 45, which aligns with the current recommendations for beginning colorectal screening. Patients with other risk factors such as family history may benefit from earlier screening. Colonoscopy for screening in average risk patients was approved by CMS for Medicare beneficiaries in 2000 and is almost universally covered by most private insurance carriers.

Alternatives Screening Methods

Colonoscopy is the gold standard when it comes to detecting and preventing colorectal cancer, especially for those with a family history of colon cancer or a history of inflammatory bowel disease. But while it's the best preventive method, many people hesitate to have a colonoscopy, often fearing the test preparation or the invasiveness of the procedure. There are other colon cancer screening tests available:

• Fecal occult blood test: The fecal occult blood test involves analyzing a stool sample (poop), for blood. Occult blood means that you can’t see it with the naked eye. Occult blood in the stool may indicate colon cancer or polyps in the colon or rectum though not all cancers or polyps bleed. One of the most performed tests is the guaiac-based fecal occult blood test (gFOBT). It uses the chemical guaiac to detect blood in the stool and it has to be done once a year.
• Fecal immunochemical test (FIT): This test uses antibodies to detect blood in the stool and it’s also done once a year.
• Stool DNA test: This test checks for blood and specific DNA in a stool sample, which could indicate the presence of colon cancer.
• Virtual colonoscopy (CT colonography): Virtual colonoscopy is a special X-ray examination of the colon using low dose computed tomography. The procedure does not require sedation. However, as with colonoscopy, a person will need to use medications or an enema to clear the colon beforehand. During the procedure, a healthcare professional will inflate the colon with air to provide a better view.

You and your doctor should decide on the method of screening based on a discussion of the benefits of each technique, possible complications, costs, availability and individual's preference.