The Food and Drug Administration on Monday approved Guardant Health’s blood test, called Shield, to screen for colon cancer. The test isn't meant to replace colonoscopies, but is generating enthusiasm among doctors who say it has the potential to boost the dismal rate of screenings for the second-highest cause of cancer death in the United States.
Shield has previously been available to doctors as a screening tool, at an out-of-pocket cost of $895. With the FDA approval, Medicare and private insurance companies are much more likely to cover the cost of the blood test, making it more widely accessible for patients.
Dr. Arvind Dasari, an associate professor in the department of gastrointestinal and medical oncology at the University of Texas MD Anderson Cancer Center, called the approval a “welcome development.”
But, he 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 American Cancer Society estimates that more than 53,000 people will die of colorectal cancer this year.
Research published in March showed Shield was 83% effective in finding colorectal cancers. It works by detecting the DNA that cancerous tumors release into the bloodstream.
It’s most effective in finding later-stage cancers, when tumors release more of that DNA. The study found that Shield only detected 13% of earlier-stage polyps.
The test would need to be given at least every three years, starting at age 45 — the same age it's recommended to begin colorectal screening.
A positive test isn’t necessarily a diagnosis. If the results indicate cancer is present, patients would still need a colonoscopy so doctors can see where tumors are and how far they’ve progressed.
“People have to understand that a positive Shield test requires a colonoscopy to confirm that you have an advanced lesion or colorectal cancer, or that the results were false,” said Robert Smith, senior vice president of Early Cancer Detection Science at the American Cancer Society. “A test like this is not complete if it’s positive and you have not had a colonoscopy.”
This is the second blood test to screen for colon cancer; Epigenomics’ Epi proColon was approved in 2016. But it’s rarely used, Smith said, because of concerns about its accuracy. It's also not covered by Medicare or private insurance.
Since the mid-1990s there’s been a troubling rise in colon cancer in people younger than 55, with rates increase increasing by 1% to 2% per year among that age group. At the same time, cases and deaths among adults 60 and older have been declining, according to the American Cancer Society.
“What breaks my heart is that it’s preventable,” said Dr. William Grady, a gastroenterologist at Fred Hutchinson Cancer Center in Seattle. “One of my biggest joys is when I’m doing colonoscopy and I can take out polyps” that, if left alone, would have progressed to cancer.
Indeed, colorectal cancer is one of the only cancers that can be prevented with screening, and colonoscopy is, by far, the most accurate way to detect it. But screening rates are extraordinarily low. Fewer than 60% of people who are eligible have had their recommended screening.
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“The biggest problem with colon cancer right now is that there’s a significant part of the population that’s not getting screened,” said Dr. Sapna Syngal, director of strategic planning for prevention and early cancer detection at the Dana-Farber Cancer Center in Boston. “If this test increases the number of people getting screened, it’s going to have a huge impact.”
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Grady, who led the March study of the Shield test, said it’s often adults in their 40s and 50s who are least likely to be compliant with screening.
“These are people who are employed, many have families, and so you have all of these other life responsibilities that get in the way of taking care of themselves, he said.
Colonoscopy is time-consuming, forcing people to take at least one day off work. There’s also a certain “ick” factor that many people find unpalatable. During the procedure, doctors insert a tiny camera into the rectum to look for tumors or spots that may become cancerous in the future.
That camera needs a clear view of the colon. The day before the colonoscopy, patients have to take a strong dose of laxatives. That is, they spend a lot of time in the bathroom.
“Many people don’t like the messiness of dealing with stool and many people really don’t like the colonoscopy — mostly the prep,” said Electra Paskett, deputy director for population sciences and community outreach at the Ohio State University Comprehensive Cancer Center. “I think a blood test would be ideal for many people.”
Another colon cancer screening method includes fecal occult blood tests that detect blood in the stool, which can be a warning sign of colon polyps or cancer. The FIT-DNA tests, such as Cologuard, are very effective at detecting cancer, but are less effective at detecting precancerous polyps.
John Gormly, 77, of Newport Beach, California, had avoided colonoscopy screening for years. When his doctor gave him the option of the Shield blood test, he took it.
“He called me a day or so later and said, ‘I don’t like the results whatsoever. I’m going to send you off to get a colonoscopy,’” Gormly recalled. “Turns out I had stage 2 colon cancer.” Surgeons were able to remove the tumor completely.
“Thank God I had taken that blood test,” Gormly said. “I never felt anything, never knew anything was wrong. Short of that blood test, I don’t know how it would have turned out.”
