In large trial, Guardant Health’s blood test detects colon cancer, but less reliably at earliest or precancerous stages

Doctors have been eagerly waiting for data on Guardant Health’s new blood-based colorectal cancer screening test, the Shield test. The hope has been that Guardant would be able to achieve an elusive goal in colorectal cancer screening: catch incipient or early colorectal cancer using nothing more than two vials of blood.

Those hopes were partially fulfilled on Wednesday. In newly published clinical trial results, the Shield test caught colorectal cancer at stages 2 or later with 100% sensitivity — but it was far worse at detecting stage 1 cancer and did not reliably detect precancerous polyps. Experts said that meant the test is likely to be an invaluable new addition to colorectal cancer screening tools and may be particularly beneficial for patients who currently choose not to get screened, but that it shouldn’t displace screening methods that can actually prevent cancer like colonoscopy.

“Over 50 million eligible Americans do not get recommended screenings for colorectal cancer, partly because current screening methods are inconvenient or unpleasant,” AmirAli Talasaz, the Guardant Health co-CEO said in a statement. “We are confident that offering an accurate blood test has the potential to significantly reduce preventable colorectal cancer deaths.”

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