By Annette Pinder

The FDA has approved a new primary screening colorectal cancer (CRC) blood test called Shield for individuals ages 45 and older at an average risk for the disease. It is the first such test to be approved as a primary screening option for CRC, but individuals with positive results will require a follow-up colonoscopy.

Shield’s safety was based on study results which showed an 83% sensitivity for CRC, and a specificity of 90% for advanced neoplasia (uncontrolled abnormal cell growth). Shield’s detection for stage I cancer was limited to 55%-65% accuracy, and was unable to detect 87% of precancerous lesions.

For those wondering why Shield would be an option despite its reduced accuracy, it helps to understand that while the national goal for CRC screening is 80%, we are far below that at only 59%. This low rate is due to many people’s unwillingness to undergo traditional screening methods, such as colonoscopy.

It is hoped that the availability of Shield will help increase the number of people who are willing to undergo testing for CRC. According to co-investigator William Grady, MD, of the Fred Hutchinson Cancer Center in Seattle, the Shield test accuracy rate is similar to that of stool tests used for early detection of CRC.

Study results were based on using Shield for adults ages 45 to 84 with an average risk for CRC. Of nearly 8,000 patients, Shield’s sensitivity for stages I, II, or III colorectal cancers was 88%, 65% for stage I cancers, 100% for stage II cancers, and 100% for stage III cancers. The test’s sensitivity was only 13% for those with precancerous lesions.

The Shield test is available by prescription, and expected to be covered by Medicare.