Despite concerns over false negative results, the Medical Devices Advisory Committee (AdCom) for the US Food and Drug Administration (FDA) has voted in favour of approving Guardant Health’s Shield blood test as a screening test for colorectal cancer.
The FDA AdCom voted 7-2 in favour of the Shield test stating that the test’s potential benefits outweighed its risks. The main point of concern was Shield’s low sensitivity in identifying early cases of colon cancer. The test has a sensitivity of 13% when identifying adenomas, which can be a precursor to colon cancer.
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The shield test was much more sensitive for identifying higher grade, grade II, or higher, colorectal cancer. It demonstrated a sensitivity of 83.1% in detecting colorectal cancer, with a 65% sensitivity for pathology-confirmed Stage I and 100% sensitivity for stage II-IV colon cancers.
It also identified bigger-sized adenomas, known as advanced neoplasia, sized 10mm or bigger with villous features or high-grade dysplasia with a sensitivity of 89.6%.
As the Shield test offers two results, negative or abnormal, the FDA was particularly concerned that an incorrect result could falsely reassure a patient of their cancer-free status and could result in patients not following up for a colonoscopy.
Colonoscopy can not only be used to identify adenomas but also to remove these before they become cancerous. Therefore, the agency was concerned that the Shield test be used as a pretest before colonoscopy and not in place of colonoscopy.
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By GlobalDataGuardant stated that the blood test offered a significant advantage over a colonoscopy or stool test as it can be easily repeated or done as part of an annual checkup. The AdCom did raise some concerns over the Shield test kit requiring four tubes of blood, stating that it was “a lot of blood” to draw from a possibly “frail” old person.
The AdCom also voted 8-1 and 6-3 in favour of the Shield test’s safety and effectiveness, respectively. The panellists noted that the test’s labelling should reflect the test’s low sensitivity in detecting advanced adenomas. Adding that Shield is a good screening test for asymptomatic colon cancer but not for adenomas and early cancer.
The AdCom is convened upon request of the FDA to review and evaluate the safety and efficacy data of a device. However, the AdCom recommendations are non-binding, with the final decision made by the agency.
