First Opinion on colorectal cancer screening: letter and response

To encourage robust, good-faith discussion about difficult issues, STAT publishes selected Letters to the Editor received in response to First Opinion essays. Today’s edition is a bit different: a letter about an essay on blood tests for detecting hidden colorectal cancer and a response from the essay’s author. Submit a Letter to the Editor here, or find the submission form at the end of any First Opinion essay.

“Balancing hope and reality: The promise and peril of blood-based colorectal cancer screening,” by Folasade P. May

I have been following the recent data releases for blood-based colorectal cancer screening tests with interest. This First Opinion essay by Dr. May accurately characterizes the potential pitfalls of a blood-based strategy; namely that it may shift the clinical performance of colorectal cancer screening programs from cancer prevention to cancer detection. This is a step backwards from current solutions and would likely increase the burden on patients and the health care system.

A strategy for screening average-risk individuals that Dr. May failed to mention is non-invasive stool-based testing. This includes both multi-target stool DNA tests (mt-sDNA) and fecal immunochemical tests (FIT). (Disclosure: My employer, Polymedco, makes such a test for colorectal cancer.) These well established and United States Preventive Services Task Force-supported methods have better sensitivity for detection of pre-malignant lesions at colonoscopy performed on “positive” patients. Thus, they are better suited to an effective prevention program.

But a major distinction between mt-sDNA tests and FIT is cost. A yearly FIT costs only tens of dollars, is easy and convenient for patients, and is supported by numerous clinical studies as being a highly cost-effective approach to identify those patients most likely to benefit from colonoscopy. sDNA tests also have a higher rate of false positives, potentially driving more people to have colonoscopies who do not need them. The so called “FIT-first” approach, using FIT in conjunction with colonoscopy, is an accurate and cost-effective way to screen populations for colorectal cancer that should not be overlooked.

As the cliché goes, the best test is the one that gets done. If blood-based screening is a more attractive option for certain patients, then it may have some utility. But as the number of individuals eligible for screening grows, we should focus on expanding use of the proven, cost-effective solutions that we already have — like FIT.

— Dr. Todd W. Kelley, Vice President of Medical Affairs, Polymedco


Dr. Folasade May responds:

Stool-based screening tests for colorectal cancer, such as the one Dr. Kelley describes, are powerful tools in the mission toward prevention and early detection, and I strongly support their use. But people who use stool-based and other non-colonoscopic tests must be aware that those are two-step tests if the result is abnormal: the individual needs to have a colonoscopy to complete the screening process. Recent national data show that only about 50% of people with an abnormal stool-based test complete a timely colonoscopy.

The adage Dr. Kelley cites, “the best test is the one that gets done,” suggests that all screening options are equivalent. With the introduction of blood-based screening options, we may need to consider whether that is still correct. Screening options currently recommended by the United States Preventive Services Task Force, including stool-based tests, colonoscopy, and CT colonography, provide the unique opportunity to both detect cancer and prevent it by leading to the removal of pre-cancerous polyps before they become cancerous. The blood-based tests for which I have seen data simply cannot do that. What we should be saying is “the best test is a test that can detect both polyps and cancers.”

— Folasade P. May, M.D., a gastroenterologist, is director of quality in digestive diseases at UCLA Health

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