FDA approves blood test to detect colon cancer for those at 'average risk'

The U.S. Food and Drug Administration on Monday morning approved a blood test to screen for colorectal cancer in certain individuals.

The blood test, known as Shield and manufactured by Guardant Health, is already commercially available, but FDA approval will help broaden availability and insurance coverage.

The test was approved for people aged 45 and older with an "average risk" of colon cancer.

Specialists warn that the blood test is not an equivalent alternative to colonoscopies, but it could lead to more people getting screened since it takes less time and effort to get screened. Colonoscopies are more accurate at detecting cancer, allow for the removal of precancerous polyps, and are recommended every 10 years instead of every three years for the blood test.

The false positive rate of the Shield test is about 10%, and it only found 13% of large polyps as compared to 95% with a colonoscopy in a clinical trial.

Shield detects colorectal cancer by detecting DNA shed by tumors in blood samples. Results take about two weeks after the samples are received by the laboratory.

Shield is not the first blood-based screening tool available for colorectal cancer, and colonoscopies are still considered the gold standard for screening.

However, the test presents another option to screen for a type of cancer that has been affecting many Americans at younger ages than before.

Earlier this year, an FDA advisory panel -- the Medical Devices Advisory Committee (MDAC) -- recommended that the federal health agency approve the test. Although FDA approval isn't guaranteed, the agency usually agrees with its advisers.

In clinical trial data, published in The New England Journal of Medicine, Shield was found to have an 83.1% sensitivity rate, meaning 83.1% of patients with colorectal cancer detected by a colonoscopy tested positive on the Shield blood test. It also had an 89.9% specificity rate, meaning 89.9% of patients without cancer tested negative on the blood test.

Despite the high overall sensitivity rate, the clinical trial data indicated Shield may miss one in 10 people who have precancerous lesions and one in 1,000 people with cancerous lesions.

These "false negatives" may result in tests finding no evidence of cancer, but patients actually have precancerous or cancerous lesions, according to the clinical trial data.

Although members of the MDAC did express concerns about false negatives, the committee ultimately found the test to be safe and effective and that the benefits of use outweighed potential risks.

"The FDA approval of the Shield test is a significant victory for patients and an important milestone in Guardant Health's mission to conquer cancer with data. Shield can help improve colorectal cancer screening rates so we can detect more cancers at an early stage, when they are treatable," AmirAli Talasaz, Guardant Health co-CEO, said in a press release.

"We are now getting ready to launch this test in the near future and are very excited to empower physicians with a viable blood-based screening option to tailor the screening regimen to the unique needs of their patients," Talasaz said.