Study details and key findings

In a clinical trial, researchers evaluated the effectiveness of a cfDNA blood-based test in 7,861 patients between the ages of 45 and 84 who had an average risk for colorectal cancer and were receiving routine colonoscopy screenings. Among the patients, the mean age was 60, and 53.7% were women.

The test, which was developed by Guardant Health, detects signs of colorectal cancer in the bloodstream by identifying circulating tumor DNA.

Overall, the researchers found that 83.1% of patients who had colorectal cancer tested positive on the blood test while 16.9% tested negative. The test had a false-positive rate of 10.1%.

The test was also able to detect 87.5% of screening-relevant colorectal cancers (stages I, II, or III). However, the test's sensitivity for advanced precancerous lesions, also known as polyps, was low at 13.2%.

Currently, Guardant sells the test as a "lab-based test," which does not require regulatory approval. However, the company has applied to FDA for approval to market the test for colorectal cancer screenings, and a decision is expected later this year.

Commentary

Colorectal cancer is the third-most diagnosed cancer in the United States, as well as the second-most common cause of cancer-related deaths. Rates of colorectal cancer are increasing among younger adults, with 20,000 U.S. adults under the age of 50 being diagnosed each year.

Early detection of colorectal cancer can prevent as many as 73% of patient deaths, but only 50% to 75% of adults who are in the recommended age range for screening get tested. Currently, the U.S. Preventive Services Task Force recommends people begin screening for colorectal cancer at age 45.

According to Barbara Jung, president of the American Gastroenterological Association, the blood test could help improve early detection of colorectal cancer. "I do think having a blood draw versus undergoing an invasive test will reach more people," Jung said. "My hope is that with more tools we can reach more people."

In addition, Jung said that she wanted to know whether the test would perform similarly in younger people who are ineligible for existing screening tests, especially since colorectal cancer rates are rising in this group. It would be "very attractive" if people in their 30s could get a blood test for colorectal cancer, Jung said. "That would be my biggest excitement."

However, Jung also noted that patients should be fully aware that, while the blood test can detect early cases of colorectal cancer, it cannot prevent them, since its sensitivity toward precancerous polyps was much lower.

"We have to have that discussion," with patients, Jung said, adding that "a lot of this will fall on primary care physicians who are already very pressed for time to get through a litany of screens and counseling."

However, John Carethers, a gastroenterologist and the vice chancellor for health sciences at the University of California, San Diego, said the ease of using the test could outweigh its potential limitations. As more people get screened with the blood test, there will be fewer colorectal cancer deaths overall.

"The best screening test is the one that gets completed by the patient," Carethers said. (Aubrey, "Shots," NPR, 3/14; Kolata, New York Times, 3/13; Bassett, MedPage Today, 3/13; Chung et al., New England Journal of Medicine, 3/14)

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