The US Food and Drug Administration has approved a blood test to be used for colorectal cancer screening among average-risk adults 45 and older – the first such test to get the green light from the FDA as a primary screening option for the cancer, which is the second most common cause of cancer deaths in the US.
The test, called Shield and made by Californian biotechnology company Guardant Health, is expected to launch commercially within the next week, and will join other types of colon and rectal cancer screening methods – including colonoscopies and at-home stool tests – as options healthcare providers can offer their patients, reports CNN.
A simple blood test may be more convenient for some patients while colonoscopies can feel invasive, or at-home stool tests can feel awkward.
“This is a promising step toward making more convenient tools available to detect colorectal cancer early while it is more easily treated,” said Dr William Grady, a gastroenterologist at Fred Hutchinson Cancer Centre.
This year, more than 53 000 people are expected to die from the disease, according to the American Cancer Society. But about 70% of colorectal cancer deaths can be prevented with increased screening.
“The test has an accuracy rate for colon cancer detection similar to stool tests used for early detection of cancer and could offer an alternative for patients who may otherwise decline current screening options,” Grady said.
Current options for colorectal cancer screening for people at average risk include a stool-based test either annually or every three years; a traditional colonoscopy every 10 years; a virtual colonoscopy every five years; or a sigmoidoscopy procedure, which involves using a tube-like instrument called an endoscope to examine the lower part of the colon, every five years.
It’s estimated that more than one in three adults, between 50 and 75, are not getting screened as recommended, according to the National Colorectal Cancer Roundtable.
The Shield blood test was already available as a laboratory-developed test or LDT before the FDA approval, but the agency’s sign-off could make the test more widely available and broadly covered as another primary screening option.
In May, the FDA’s Molecular and Clinical Genetics Panel of the Medical Devices Advisory Committee voted 8-1 that the Shield test was safe for use in people who meet the criteria for testing, 6-3 that the test is effective for use in those meeting the criteria and 7-2 that the benefits of the test outweigh the risks.
It works by detecting tumour DNA in blood samples, and a physician would need to order the test and kit for patients.
The test was found to have around 83% sensitivity and 90% specificity in a study, which included nearly 8 000 people, published in March in the New England Journal of Medicine. Sensitivity refers to a test’s ability to accurately identify people with disease, designating them as positive. Specificity refers to its ability to accurately designate people without a disease as negative.
The study found that about 83% of participants who had been diagnosed with colorectal cancer via colonoscopy tested positive for the disease on the Shield test, compared with about 17% who had a false negative.
The test showed about 88% sensitivity in detecting stage I, II or III colorectal cancer and a lower sensitivity, around 13%, in detecting precancerous lesions.
About 90% of the study participants without advanced colorectal cancer or precancerous lesions tested negative on the blood test, compared with about 10% who had a false positive test result.
Separately, several research teams and companies have been working to develop simple blood tests to screen for colon and rectal cancers.
“The argument is that a point-of-care blood test can actually significantly reduce the incidence rate of very advanced disease and save lives, even if it has lesser potential to prevent the disease,” Robert Smith, senior vice-president of early cancer detection science at the American Cancer Society, said in May.
A blood-based test would not be able to identify concerning lesions or polyps in the colon or rectum, as a colonoscopy would. With visual exams, like colonoscopies or sigmoidoscopies, a lesion or polyp that has the potential to develop into cancer can be identified and removed, thus preventing the disease.
“Most people would like to see a blood-based option that was more accurate with respect to finding precursor lesions in addition to cancers. But the rather remarkable thing about colorectal cancer screening is that people vary in their readiness to do one test or another,” Smith said. “You have to give people a choice.”
See more from MedicalBrief archives:
Updated US guidelines for colorectal cancer screenings
More younger people being diagnosed with colorectal cancer
Colonoscopy may not be gold standard of colon cancer screening – large randomised trial