Around 150,000 Americans are diagnosed with colon cancer every year, and as the country's second-leading cause of cancer deaths, it kills about 50,000 people annually, according to the American Cancer Society. Colon cancer is usually diagnosed with a colonoscopy. A new colon cancer blood test has been developed by a company called Guardant Health, and it's called Shield. The company maintains that the blood test could identify people who are only at average risk of colon cancer, but who might not be screened with a colonoscopy for some reason.
Right now, a colonoscopy is still considered to be the best way to diagnose colon cancer. But colonoscopies can be challenging for some individuals; they are extremely invasive, they require patients to consume a preparatory drink that has a very unpleasant reputation, and since strong sedatives are used during the procedure, the patient must have someone with them who can take them home from their appointment. There may be people who are opting to forego a colon cancer screening, or putting one off, because of these requirements.
This (second) blood test for colon cancer has now been approved by a US Food and Drug Administration (FDA) advisory panel. The decision was not unanimous, with seven of nine individuals on the panel voting that the benefits of this test do outweigh the risks. This panel is intended to offer non-binding advice for the FDA in its ultimate approval decision, and a final answer is expected later this year as the FDA weighs this advice and other factors. The panel also voted eight to one that Shield is safe, and six to three that it is effective.
"Despite the importance of detecting colorectal cancer early, there are notable barriers that can deter average-risk Americans from completing existing screening methods," said the co-CEO of Guardant Health, AmirAli Talasaz. The company noted that this test might prevent colon cancer deaths in individuals who are unable to get a colonoscopy.
There is also a fecal test for colon cancer, but blood-based tests are considered far more convenient.
If the FDA ultimately approves Shield for the market, it will be the second blood test for the disease in the US, after Epi proColon by Epigenomics.
A concern, however, is that Shield is simply not as accurate as a colonoscopy. The test was only able to detect 13 percent of advanced adenomas, which are pre-cancerous tumors. In evaluations, Shield was able to identify colon cancer 83 percent of the time, so it also misses some instances of the disease.
NBC News reported on the FDA panel meeting. One panelist, Professor Charity Morgan of the University of Alabama, noted that Shield "is better than nothing, but I don't want to downplay the issue that this test is going to miss a lot of cancers." The company's response was to suggest that the test be taken every one to three years, and that colonoscopies should still be "prioritized" for patients.
Sources: FDA, Guardant Health