Blood tests for colon cancer not ready to replace colonoscopy, study shows

New blood tests screen for colorectal cancer in a much less invasive way than colonoscopy, but deaths will increase if many people choose this alternative, a new study indicates.

The study was published Monday in Annals of Internal Medicine.

Blood tests are emerging as an innovative tool for colorectal cancer detection because they have the potential to save lives compared with no screening. For now, however, patients should stick with more proven techniques, researchers said.

“The development of blood tests to screen for cancer is a true scientific breakthrough that could completely change the world of cancer screening,” the study’s lead author, Dr. Uri Ladabaum, director of the Gastrointestinal Cancer Prevention Program at Stanford Medicine in Palo Alto, Calif., told UPI.

“But the first-generation blood tests for colorectal cancer are not as good as our current alternatives,” Ladabaum said.

Researchers also determined that colonoscopies — and stool screening — were more cost-effective than blood tests.

But blood tests will help decrease colorectal cancer deaths only if patients do them every three years and proceed to colonoscopy after a positive result, Ladabaum noted.

“People should think carefully about the relative expected benefits of the various screening options, and how they value that compared to convenience,” he said.

With current screening and prevention efforts, about 4% of American adults will receive a colorectal cancer diagnosis. Regular screening can help find cancer early, as well as precancerous polyps, lowering the risk of developing the disease and dying.

The U.S. Preventive Services Task Force recommends that all adults between the ages of 45 and 75 undergo colorectal cancer screening.

For a long time, screening has consisted of either colonoscopy once every decade or a stool test every one to three years. While the exam can detect colorectal cancer, it also can prevent it if the clinician removes precancerous polyps.

However, about 1 in 3 American adults in the recommended age range has not had any colorectal cancer screening, so experts hope new options could persuade them to pursue testing.

To compare the effectiveness of different screening methods, researchers gathered previously published data on six commercially available or in-development blood- and stool-based tests, as well as colonoscopy.

They found that among 100,000 average-risk people who undergo colonoscopy every 10 years, 1,543 would develop colorectal cancer and 672 would die.

“This population-wide uptake of colonoscopy is unrealistic,” Ladabaum said. “That is why there is such intense interest in novel, noninvasive alternatives.”

The number of people who develop cancer after screening with the new blood tests is much higher — between 4,310 and 4,365, he said. These tests are recommended every three years.

Meanwhile, about 2 1/2 times as many people — 1,604 to 1,679 — died from colorectal cancer in the blood-testing group than in the colonoscopy group.

The projections for the blood tests are still considerably lower, though, than the rates among people who skip all screening. In this no-testing scenario, 7,470 would develop colorectal cancer and 3,624 would die.

“Screening with the first-generation of blood tests is substantially better than no screening at all,” Ladabaum said. “But for now, the established stool tests and screening colonoscopy remain the most effective and cost-effective options.”

Other gastrointestinal specialists highlighted the study’s value in comparing different screening modalities for colorectal cancer.

Dr. Jatin Roper, a spokesperson for the American Gastroenterological Association, told UPI that most people age 45 or older are eligible for colorectal cancer screening. He was not involved in conducting the research.

“This study will help them and their doctors decide which test to get,” said Roper, who also is a gastroenterologist and gastrointestinal cancer geneticist at Duke University School of Medicine in Durham, N.C.

“Most important, this study will help health care administrators decide on coverage for new colorectal cancer screening tests,” he said.

Dr. Lilian Chen, chief of colon and rectal surgery at Tufts Medical Center in Boston, said some patients are at higher risk of complications from colonoscopy.

“I think that if the patient, for whatever reason, is not willing to complete a stool test or colonoscopy, this blood test may be a reasonable alternative” to begin screening and then follow up with a colonoscopy if the result is abnormal.

“Colonoscopy is still the gold standard for colorectal cancer screening,” Dr. Jacquelyn Turner, section chief of colon and rectal surgery at Tulane School of Medicine in New Orleans, said while noting that it’s better at detecting stage 1 cancer, as well as polyps.

“The other screening tests are positive once a mass is big enough to bleed or shed DNA cells,” Turner said.

“In other words, the next-generation tests are good for detecting cancer after it has already developed,” she said. “Again, the difference between cancer prevention and cancer detection should be highlighted and explicitly explained to patients.”