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New blood-based screening tests for colorectal cancer (CRC) offered fewer benefits at higher cost versus other screening options, a cost-effectiveness modeling study suggested.

In a comparison against multiple alternative screening strategies, a cell-free DNA blood test (cf-bDNA) prevented the fewest cancers and cancer-specific deaths versus no screening. With an estimated cost of almost $90,000 per quality-adjusted life-year (QALY) gained, the Guardant Shield blood test also had the highest cost among available options.

Decreasing the recommended screening interval from 3 years to 2 or 1 improved the cfDNA prevention metrics but at substantially greater cost, reported Uri Ladabaum, MD, of Stanford University in California, and co-authors in the .

"First-generation novel cf-bDNA tests have the potential to decrease meaningfully the incidence and mortality of CRC compared with no screening, but substantially less profoundly than screening colonoscopy or stool tests," the authors concluded. "Net population benefit or harm can follow incorporation of first-generation cf-bDNA CRC screening tests into practice, depending on the balance between bringing unscreened persons into screening (addition) versus shifting persons away from the more effective strategies of colonoscopy or stool testing (substitution)."

"In clinical settings with multiple CRC screening options, shared decision making should consider all of the attributes of competing strategies, including test performance characteristics and cost, and the need for colonoscopy follow-up after an abnormal noninvasive screening test must be emphasized," they stated.

A study limitation is the focus on one type of test versus none. In the U.S., patients have options for CRC screening. The American Cancer Society (ACS) recommends that clinicians offer patients the option of a stool test or direct visual examination, depending on the path the patients want to take, and then consider the testing options, said Robert Smith, PhD, senior vice president for early cancer detection science at the ACS.

"What we've learned over the years is that some patients are averse to an invasive procedure, or that [the discussion of colonoscopy] just sort of goes in one ear and out the other," Smith told MedPage Today. "Or they might be committed to doing it but when they start to take the steps, it becomes too complicated, and so it doesn't happen."

Offering patients the options of a multi-target stool DNA test, fecal immunochemical test (FIT), or colonoscopy has been shown to improve screening rates.

"Someone who doesn't want a colonoscopy quite often will do a stool test," said Smith.

The new cfDNA blood tests have introduced another consideration into the process. The idea of adding a CRC screening test to other routine blood work appeals to many patients and clinicians alike.

A key limitation of cfDNA tests is their relatively low sensitivity for stage I cancers and advanced colorectal polyps, which can evolve into cancer.

"They have poor sensitivity for advanced adenomas, where colonoscopy has pretty good sensitivity for those because it's a direct visual examination," said Smith. "We remove those polyps and then they don't become colorectal cancer. We have seen a significant drop in the incidence of disease because colonoscopy is the dominant test that is used in this country."

Smith agreed with the study authors that cf-bDNA tests are "expensive" and "not as cost effective."

"The other concern is what happens when a patient says, 'You're drawing blood on me anyway, so you can just give me this blood test and I'll be done with colorectal cancer screening,'" he added. "You lose the advantage of prevention."

The cost-effectiveness analysis was based on the Model of Screening and Surveillance for Colorectal Cancer, a for conducting studies of CRC incidence and mortality and cost-effectiveness of screening tests. The study focused on average-risk adults ages 45-100.

Investigators evaluated seven different screening tests: the Guardant Shield cf-bDNA test (FDA approved earlier this year), an investigational cf-bDNA test, the Cologuard stool DNA test, an investigational , FIT testing, FIT DNA testing, FIT RNA testing, and colonoscopy. Testing intervals were annual with standard FIT, every 10 years with colonoscopy, and every 3 years with all the other tests.

All of the tests were compared against no screening. The analyses produced the following relative rates (RR) for CRC incidence and mortality, respectively:

• Colonoscopy: RR 0.21, 0.19
• Annual FIT: RR 0.29, 0.25
• Stool DNA: RR 0.33, 0.28
• FIT RNA: RR 0.32, 0.28
• Guardant Shield cf-bDNA: RR 0.58, 0.44
• Investigational cf-bDNA: RR 0.58, 0.46

In the cost-effectiveness analysis, colonoscopy and annual FIT emerged as the dominant (favored) strategies. The estimated cost per QALY was $6,300-$6,500 with the two stool DNA tests and $89,600 with the Guardant Shield. Cost-effectiveness could not be calculated at this point for the investigational cf-bDNA and the FIT RNA tests.

As a final thought on the study and CRC screening in general, Smith quoted long-time NIH scientist and CRC screening pioneer : "The best test is the one you get."

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