Can a Blood Test Detect Colorectal Cancer?

By Pat Carragher - March 19, 2024

As the number of colorectal cancer cases rise, so does the need for new and better ways to detect the disease. A recent study shows that help could be on the way. Results of a clinical trial published in The New England Journal of Medicine show that a blood-based screening test detected colorectal cancer in 83% of people with the disease.

The test is performed using a simple blood draw. Once the sample is collected, it’s examined to find cancer cells left behind in the bloodstream called circulating tumor DNA (ctDNA).

While the test could add a valuable tool in the fight against colorectal cancer if approved by the U.S. Food and Drug Administration, doctors say a screening colonoscopy is still the gold standard when it comes to detecting and preventing disease.

“In an ideal world, everyone goes to get a first colonoscopy at age 45. That’s not going to happen,” Dr. Tiago Biachi, a gastrointestinal oncologist at Moffitt Cancer Center, said in a recent interview with NBC News. “But if these blood tests can lead to getting more people in the door for a colonoscopy, that’s a good thing.”

Dr. Tiago Biachi, Department of Gastrointestinal Oncology
Dr. Tiago Biachi, Department of Gastrointestinal Oncology

In 2022, the U.S. Preventive Services Task Force recommended that people of average risk start colorectal cancer screenings at age 45. This includes people with no prior diagnosis of colorectal cancer, no family history or genetic disorders that increase your risk of disease, no history of precancerous polyps and no diagnosis of inflammatory bowel disease.

More than 1 in 3 eligible adults are not screened as recommended, according to the American Cancer Society.

While a blood test may be less invasive than a colonoscopy, it can detect cancer only when it’s already developed. During a colonoscopy doctors can find and remove polyps five to 10 years before they potentially turn into cancer.

In addition to colonoscopy, other recommended screenings include computed tomography colonography and stool-based tests with high sensitivity such as fecal immunochemical tests (FIT) that are widely accessible and would require a colonoscopy follow-up if the test comes back abnormal.

A positive blood test isn’t an official diagnosis, so anyone who tests positive would need a colonoscopy to confirm if there is disease. In addition, only a colonoscopy can tell doctors where tumors are hiding in the colon.

“The location of colorectal tumors can determine whether patients need surgery or chemotherapy and radiation before surgery,” Biachi said. “This blood test is not a home run for cancer diagnosis.”

The FDA is expected to consider the blood test for approval this year, according to the manufacturer.

If approved, the test would be given every three years starting at age 45. People with symptoms of colon cancer or a family history of the disease should still speak with their doctor about a colonoscopy.

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