Q&A: 'Convenience is a major selling point' for new colorectal cancer blood test

Key takeaways:

• The FDA approved the first blood test as a primary colorectal cancer screening option in line with other noninvasive alternatives.
• An expert described the pros and cons for the test, its cost and more.

The new blood test screening option for colorectal cancer is innovative and could improve screening uptake, but it also has some drawbacks, according to an expert.

In late July, the FDA approved the first blood test as a primary colorectal cancer (CRC) screening option in line with other noninvasive alternatives. Shield, from Guardant Health, is also the first blood test to meet the performance requirements to be covered under Medicare. It is intended for patients aged 45 years and older at average risk for developing the disease.

Healio spoke with Robert Smith, PhD, senior vice president of early cancer detection science at the American Cancer Society, to learn about the new blood test, who primary care providers should recommend it to and more.

Healio: Considering colonoscopies are the first choice of frontline CRC screening tools , what is this new blood test for?

Smith: We do use colonoscopy as a benchmark for the performance of noncolonoscopy tests because an individual with a positive finding will need to undergo a colonoscopy to determine whether they have advanced neoplasia or cancer, which is the case for all noncolonoscopy CRC screening tests that are positive. Colonoscopy was the follow-up test that determined the accuracy of the SHIELD test. But colonoscopy is very operator dependent, and thus, it is not a perfect test. Sometimes examiners miss important lesions, sometimes they fail to examine the entire colon, sometimes they fail to meet quality assurance standards for withdrawal time. But the target population tends to choose different tests. Not all adults want, or are willing, to undergo a colonoscopy. Not all individuals can get a colonoscopy easily because the need to take 1 or 2 days off work and have a chaperone bring them home after having undergone sedation. Roughly half of adults are not presently adherent with recommendations for regular CRC screening. The developers of the test believe that a point-of-care test that can be done with a single blood test could increase screening rates. The little evidence we have suggests that this is true. The SHIELD test should be presented to patients as a test that has good accuracy in finding CRC, but it has poor performance in finding adenomas, which are precursor lesions for CRC. Thus, compared with other CRC screening tests, it does not excel at preventing CRC through the identification of precancerous lesions that, when removed, can stop that lesion from becoming cancerous.

Healio: What should PCPs know about the pros and cons of this new option?

Smith: The pros are that if you have not ever been screened, or not recently screened for CRC, it is a simple test that can be done in the doctor's office. Convenience is a major selling point, and compared with colonoscopy, no bowel cleansing (the prep), no sedation, no time off from work and no need to find someone to drive you home. It also has good sensitivity for CRC, and although some of the cancers it detects are advanced, it still is better to find them earlier than will be the case if no screening takes place.

The cons are the data showing that the test has poor performance at finding precancerous lesions, and thus will not prevent many CRCs by delivering a positive finding, resulting in a colonoscopy, which would likely pick up the precancerous lesion [that] can be removed. The test is also expensive.

Healio: How much will the test cost?

Smith: In July 2024, the price of the test was quoted to be $895. The price may have changed since then.

Healio: If patients choose this option over colonoscopy, how often should they get this test done?

Smith: At this time, Guardant is recommending screening with the SHIELD test at least every 3 years.

Healio: What is the take-home message for PCPs here?

Smith: The FDA has approved the test, and it is covered by Medicare. However, no guideline-developing organization has reviewed the evidence for the SHIELD test and issued a guideline recommending or not recommending it. The SHIELD test may appeal to patients who have never undergone testing, or who have been tested before but are not currently adherent with recommendations for screening. PCPs should discuss the benefits and limitations of the test with their patients, especially that the test compares poorly with other tests at preventing CRC. If the patient is not covered by Medicare, then they should determine if their health plan would cover the test — otherwise, it would be an out-of-pocket cost.

Healio: Is there anything else you would like to add?

Smith: With respect to CRC, we have long said that the best test is the one that the patient is willing to get.