Blood-Based Screening for Colorectal Cancer Promising but Still Lacks Robust Efficacy

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Blood-based screening for colorectal cancer (CRC), also known as a "liquid biopsy," may be better than nothing among patients who skip established screening tests, but it can't replace colonoscopy as the gold standard, according to two new modeling studies and an expert consensus commentary.

Although some patients find blood-based tests more convenient, the higher numbers of false positives and false negatives could lead to more CRC cases and deaths.

"Based on their current characteristics, blood tests should not be recommended to replace established colorectal cancer screening tests, since blood tests are neither as effective nor cost-effective and would worsen outcomes," David Lieberman, MD, AGAF, chair of the American Gastroenterological Association's CRC Workshop Panel, and lead author of the expert commentary, said in a statement.

The blood tests detect circulating nucleotides, such as cell-free DNA or metabolic products associated with CRC and its precursors. Current tests are in development by Guardant Health and Freenome.

The two modeling studies, published in Gastroenterology on March 26, analyzed the effectiveness and cost-effectiveness of blood-based CRC screening that meets Centers for Medicare & Medicaid Services (CMS) coverage criteria, as well as the comparative effectiveness and cost-effectiveness of CRC screening with blood-based biomarkers versus fecal tests or colonoscopy.

Also published on March 26 in Clinical Gastroenterology and Hepatology, the expert commentary included key conclusions from the AGA CRC Workshop, which analyzed the two modeling studies.

Comparing CRC Screening Methods

In the first modeling study, an international team of researchers ran three microsimulation models for CRC to estimate the effectiveness and cost-effectiveness of triennial blood-based screening for ages 45-75, compared with no screening, annual fecal immunochemical testing (FIT), triennial stool DNA testing combined with a FIT assay, and colonoscopy screening every 10 years. The researchers used CMS coverage criteria for blood tests, with a sensitivity of at least 74% for detection of CRC and specificity of at least 90%.

Without screening, the models predicted between 77 and 88 CRC cases and between 32 and 36 deaths per 1,000 individuals, costing between $5.3 million to $5.8 million. Compared with no screening, blood-based screening was considered cost-effective, with an additional cost of $25,600 to $43,700 per quality-adjusted life-year gained (QALYG).

However, compared with the FIT, stool, and colonoscopy options, blood-based screening was not cost-effective, with both a decrease in QALYG and an increase in costs. FIT was more effective and less costly, with 5-24 QALYG and nearly $3.5 million cheaper than blood-based screening, even when blood-based uptake was 20 percentage points higher than FIT uptake.

In the second modeling study, US researchers compared triennial blood-based screening with established alternatives at the CMS thresholds of 74% sensitivity and 90% specificity.

Overall, a blood-based test at the CMS minimum reduced CRC incidence by 40% and CRC mortality by 52% versus no screening. However, a blood-based test was significantly less effective than triennial stool DNA testing, annual FIT, and colonoscopy every 10 years, which reduced CRC incidence by 68%-79% and CRC mortality by 73%-81%.

Assuming a blood-based test would cost the same as a multi-target stool test, the blood-based test would cost $28,500 per QALYG versus no screening. At the same time, FIT, colonoscopy, and stool DNA testing were less costly and more effective. In general, the blood-based test would match FIT's clinical outcomes if it achieved 1.4- to 1.8-fold the participation rate for FIT.

Even still, the sensitivity for advanced precancerous lesion (APL) was a key determinant. A paradigm-changing blood-based test would need to have higher than 90% sensitivity for CRC and 80% for APL, 90% specificity, and cost less than $120 to $140, the study authors wrote.

"High APL sensitivity, which can result in CRC prevention, should be a top priority for screening test developers," the authors wrote. "APL detection should not be penalized by a definition of test specificity that focuses on CRC only."

Additional Considerations

The AGA CRC Workshop Panel met in September 2023 to review the two modeling studies and other data on blood-based tests for CRC. Overall, the group concluded that a triennial blood test that meets minimal CMS criteria would likely result in better outcomes than no screening and provide a simple process to encourage more people to participate in screening.

However, patients who may have declined colonoscopy should understand the need for a colonoscopy if blood-based tests show abnormal results, the commentary authors wrote.

In addition, because blood-based tests for CRC appear to be less effective and more costly than current screening options, they shouldn't be recommended to replace established screening methods. Although these blood-based tests may improve screening rates and outcomes in unscreened people, substituting blood tests for other effective tests would increase costs and worsen patient outcomes.

Beyond that, they wrote, the industry should consider other potential benchmarks for an effective blood test, such as a sensitivity for stage I-III CRC of greater than 90% and sensitivity for advanced adenomas of 40%-50% or higher.

"Unless we have the expectation of high sensitivity and specificity, blood-based colorectal cancer tests could lead to false positive and false negative results, which are both bad for patient outcomes," John M. Carethers, MD, AGAF, vice chancellor for health sciences at UC San Diego, AGA past president, and a member of the AGA CRC Workshop panel, said in a statement.