The United States Food and Drug Administration (FDA) approved a new blood test to screen for colon cancer on July 29. The test from Guardant Health called Shield is not intended to replace colonoscopies that screen for the second-highest cause of cancer death in the US.
Previously, the blood test has been available as a screening tool and cost patients $895 out-of-pocket. The new approval from the FDA means that private insurance companies and Medicare are significantly more likely to cover the costs and make it more accessible.
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Shield requires one sample of blood for the process of detecting early-stage cancers that are typically more curable. However, it has a poor record of detecting precancerous growths. Other screening tests including colonoscopies or fecal sample tests used to find colon and rectal cancer have a better record at detecting precancerous growths. Removing these growths early can help prevent cancer.
Even with this limitation, the hope is that Shield will encourage more people to get screened. Shield is currently approved for people 45 and older who are at average risk for colon cancer. According to American Cancer Society estimates, 53,000 Americans are expected to die from colorectal cancers this year alone. Colon cancer has also risen in those younger than 55 by one to two percent since the mid-1990s. Cases in adults 60 and older have been declining in that same time period. Regular screening can prevent up to 73 percent of colon cancer deaths. While current guidelines recommend that testing begins at age 45.
Shield works by detecting DNA fragments from cancer cells or the clumps of cells in the lining of the colon that can turn into cancer called polyps in the blood. Detecting the cancerous DNA fragments released into the bloodstream can detect the presence of some cancers or serious polyps.
In a study published in March, Shield was 83 percent effective in finding colorectal cancers. It is most effective in finding later-stage cancers. This is when tumors release more of that DNA into the blood. It only detected 13 percent of earlier-stage polyps, compared with 95 percent of colonoscopies. Shield also had a false positive rate of 10 percent.
Dr. Arvind Dasari from the department of gastrointestinal and medical oncology at the University of Texas MD Anderson Cancer Center, told NBC News that the approval is a “welcome development.” However, Dasari cautioned, “we’ll have to wait and see what the impact will be in terms of improving screening and reducing the incidence of mortality.”
The nature of colon and rectal cancer screenings, which can be uncomfortable for some, remains a challenge in convincing patients to get tested. Fecal tests examine the feces for possible signs of colorectal cancer or polyps. While they can be completed at home, they require patients to male samples of feces to a lab. Colonoscopies are often avoided due to the preparation and the idea of having a tube with a camera inserted into the rectum and large intestine. Preparing for it can require up to 24 hours of fasting, followed by a powerful laxative to clear out the colon. Patients also often lose a day of work since the procedure requires anesthesia.
Doctors recommend that most people begin colorectal cancer screening by age 45, but those with higher risk may start earlier. Despite tests being very good at detecting cancer, less than 60 percent of those eligible have had the recommended screening.
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“The persistent gap in colorectal cancer screening rates shows that the existing screening options do not appeal to millions of people,” Daniel Chung, MD, a gastroenterologist at Massachusetts General Hospital and Professor of Medicine at Harvard Medical School, said in a press release. “The FDA’s approval of the Shield blood test marks a tremendous leap forward, offering a compelling new solution to close this gap. This decision will help make screening tests more broadly accessible and propel blood-based testing and CRC screening into a new era. With increased screening rates and early cancer detection, many more lives can be saved.”
Shield is currently the second blood test to screen for colon cancer. In 2016, the FDA approved Epigenomics’ Epi proColon. However, the test is not widely used due to concerns about its accuracy and it is not covered by either private insurance or Medicare.
According to Guardant Health, the test meets Medicare’s requirements for coverage. Patients covered by Medicare part B will not see an additional cost. The out of pocket cost for those with Medicare Advantage or private insurance will depend on the plan.