Finally, a Simple Blood Test for Colorectal Cancer Screening

FINALLY, A SIMPLE BLOOD TEST FOR COLORECTAL CANCER SCREENING

I recently read that the U.S. Food & Drug Administration (FDA) has approved the first-ever blood test for colorectal cancer screening. This test, called Shield, is a game-changer because FDA approval means it will likely be covered by many insurance plans. For those with Medicare Part B, there are no out-of-pocket costs, while Medicare Advantage enrollees may only need to provide a co-pay.

Interestingly, during my annual wellness visit with my primary care doctor last week, she recommended I get screened for colorectal cancer, as it had been a while since my last tests. I remembered going through a lengthy prep plus the actual colonoscopy procedure a few years ago and since then collecting a stool sample at home and sending it to a lab every couple of years. Naturally, I was thrilled to hear about the availability of a simple blood test as an alternative.

For additional details, please refer to these excerpts from a CNN online article by Jacqueline Howard, published on July 19, 2024, titled FDA approves blood test for colorectal cancer screening among average-risk adults in the US.

The US Food and Drug Administration has approved a blood test to be used for colorectal cancer screening among average-risk adults 45 and older.

The maker of the test, Palo Alto, California-based biotechnology company Guardant Health, announced Monday that this is the first blood test to be approved by the FDA as a primary screening option for colorectal cancer, and it’s the first approved blood screening test for colorectal cancer.

In the United States, colorectal cancer is the second most common cause of cancer deaths, and this year more than 53,000 people are expected to die from the disease, according to the American Cancer Society. But about 70% of colorectal cancer deathscan be prevented with increased screening.

The test, which has an accuracy rate for colon cancer detection similar to stool tests used for early detection of cancer, could offer an alternative for patients who may otherwise decline current screening options.

Current options for colorectal cancer screening for people at average risk include a stool-based test done either annually or every three years; a traditional colonoscopy every 10 years; a virtual colonoscopy every five years; or a sigmoidoscopy procedure, which involves using a tube-like instrument called an endoscope to examine the lower part of the colon, every five years.

Many Adults are Not Getting Screened

It’s estimated that more than 1 in 3 adults, ages 50 to 75, are not getting screened as recommended, according to the National Colorectal Cancer Roundtable. The US Preventive Services Task Force recommends that screening for colorectal cancer start at age 45 for people at average risk.

“The persistent gap in colorectal cancer screening rates shows that the existing screening options do not appeal to millions of people,” Dr. Daniel Chung, gastroenterologist at Massachusetts General Hospital and Professor of Medicine at Harvard Medical School, said in a statement released Monday by Guardant Health.

“The FDA’s approval of the Shield blood test marks a tremendous leap forward, offering a compelling new solution to close this gap. This decision will help make screening tests more broadly accessible,” Chung said. “With increased screening rates and early cancer detection, many more lives can be saved.”

In the United States, about 1 in 23 men and 1 in 25 women will be diagnosed with colorectal cancer in their lifetime.

How the Shield Blood Test  Works

The Shield test works by detecting tumor DNA in blood samples, and a physician would need to order the test and kit for their patient.

The test was found to have around 83% sensitivity and 90% specificity in a study, which included nearly 8,000 people, published in March in the New England Journal of Medicine. Sensitivity refers to a test’s ability to accurately identify people with disease, designating them as positive. Specificity refers to its ability to accurately designate people without a disease as negative.

The study found that about 83% of participants who had been diagnosed with colorectal cancer via colonoscopy tested positive for the disease on the Shield test, compared with about 17% who had a false negative.

The test showed about 88% sensitivity in detecting stage I, II or III colorectal cancer and a lower sensitivity, around 13%, in detecting precancerous lesions called polyps.

 “The argument is that a point-of-care blood test can actually significantly reduce the incidence rate of very advanced disease and save lives, even if it has lesser potential to prevent the disease,” Robert Smith, senior vice president of early cancer detection science at the American Cancer Society, said in May.

A blood-based test would not be able to identify concerning lesions or polyps in the colon or rectum, as a colonoscopy would. With visual exams, like colonoscopies or sigmoidoscopies, a lesion or polyp that has the potential to develop into cancer can be identified and removed, thus preventing the disease.

“Most people would like to see a blood-based option that was more accurate with respect to finding precursor lesions in addition to cancers. But the rather remarkable thing about colorectal cancer screening is that people vary in their readiness to do one test or another,” Smith said. “You have to give people a choice.”