Colonoscopy Still Beats New Blood Tests at Spotting Colon Cancer

October 29, 2024
Dennis Thompson HealthDay Reporter

Middle-aged folks facing a colon cancer screening now have a blood test they can choose over a standard colonoscopy.

However, the blood test isn't as effective as colonoscopy at detecting and preventing colon cancer, a new review finds.

About two and a half times more colon cancer deaths can be expected to occur in people taking the blood test every three years as recommended, compared to those who undergo colonoscopy once a decade.

Colon cancer death rates will increase if too many people choose the blood test over either colonoscopy or stool-based tests, researchers predicted.

“The first generation of blood tests are a really exciting development in the colorectal cancer screening paradigm,” said lead researcher Dr. Uri Ladabaum, a professor of gastroenterology with Stanford Medicine. “But for now, if you’re willing and able to do a colonoscopy or stool-based test, don’t switch to a blood test.”

The U.S. Food and Drug Administration in July approved the first blood test for screening colon cancer in people at average risk of the disease.

The FDA based its approval on a clinical trial involving nearly 8,000 people, which found that the test detected colon cancer in more than 83% of people with a colorectal tumor.

However, the test only was able to detect precancerous colon polyps in about 13% of people.

Colonoscopy is not an easy procedure. People must take powerful laxatives ahead of time to completely empty their bowels, and are put under sedation while doctors use a thin tube to examine the inside of the entire colon.

However, colonoscopy makes colon cancer one of the only fully preventable cancers, because doctors can remove any precancerous polyps they come across during the examination.

“This makes colonoscopy a unique cancer screening method because you also have the possibility of cancer prevention,” Ladabaum said. “Despite that, there are many people who are not getting screened at all, or who are not getting screened as often as they should.”

Patients who get a positive result from a fecal or blood test are urged to undergo colonoscopy, to double-check whether they have either cancer or polyps.

For the study, researchers pooled together data on six commercially available or in-development blood- and stool-based screening tests, as well as on gold-standard colonoscopy.

Using this data, they estimated the relative rate of colon cancer cases and deaths among people who used each screening approach.

The estimated case and death rate for every 100,000 people who choose:

Colonoscopy -- 1,543 cases and 672 deaths
Stool tests -- about 2,200 to 2,500 cases and 904 to 1,025 deaths
Blood tests -- about 4,300 cases and 1,600 deaths
No screening -- 7,500 cases and 3,600 deaths

Researchers also found that colonoscopies and stool tests are more cost-effective than blood tests.

The study was published Oct. 28 in the Annals of Internal Medicine.

“The blood tests are certainly much better than nothing, but you’ll worsen the population outcomes and raise health care costs if you see people switching from colonoscopies to first-generation blood tests,” Ladabaum said in a Stanford Medicine news release.

The best-case scenario will be if most people continue to use colonoscopy or fecal tests, and resort to a blood test only if they find those two options so repellant they would otherwise not be screened, researchers said.

“Ideally, we want as many people as possible to get screened for colorectal cancer, and that’s likely going to mean a combination of different tests being used across the population,” Ladabaum said.

However, the blood test is still so new that it isn’t covered by existing colon cancer screening guidelines, and it’s not clear how many people will choose it, researchers noted.

“It remains to be seen who will really use the blood tests,” Ladabaum said. “Will it be people who have never been screened using any other method? And will they be willing to get a follow-up colonoscopy if indicated?”

More information

The U.S. Centers for Disease Control and Prevention has more on colon cancer screening.

SOURCE: Stanford Medicine, news release, Oct. 28, 2024

Cancer: Colon Colonoscopy