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Blood tests may soon be an option for colorectal cancer screening. Photo by Dominika Zarzycka/NurPhoto via Getty Images
  • Researchers are reporting that a new home blood test for colorectal cancer is as accurate as current home tests using stool samples.
  • Doctors say they hope a new test such as this one would encourage more people to get tested for colorectal cancer early.
  • In a new commentary a panel of experts said blood tests aren’t as effective as current screening methods and shouldn’t be used as a replacement for those tests.

The home-based test for colorectal cancer can be unpleasant.

Not that having one’s blood drawn is the most pleasing experience either. However, for those who dislike the home stool test, there’s now evidence a new blood test might be just as effective as that stool test.

Both are about 83 percent accurate, according to a new study published in the New England Journal of Medicine.

Researchers note that number applies to people of average risk who are not experiencing symptoms. The percentage is also lower than the accuracy of colonoscopies.

“The results of the study are a promising step toward developing more convenient tools to detect colorectal cancer early while it is more easily treated,” said Dr. William Grady, a study author and a gastroenterologist at Fred Hutchinson Cancer Center in Seattle, in a statement. “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.”

In a new commentary, a panel of experts stated that the new blood tests aren’t as effective as current screenings and also aren’t cost-effective. They did say that the blood tests are better than a person not getting screened at all.

The new findings were the result of the ECLIPSE study, a multisite clinical trial that looked at test results of nearly 8,000 people, ages 45 to 84.

The ECLIPSE study compared colonoscopies – which are currently considered the best way to detect colon cancer – to the Guardant’s Shield blood test.

The shield test detects colorectal cancer signals in blood DNA shed by tumors, something called circulating tumor DNA (ctDNA). That measurement is also used in liquid biopsy tests used in monitoring for cancer recurrence in people who have already had cancer. It’s also used for other emerging cancer screening tests, the authors noted.

Of the 7,861 people looked at by researchers, 83% of participants with colorectal cancer confirmed by a colonoscopy had a positive blood test for ctDNA while 17% had a negative test. The latter group had colorectal cancer as confirmed by biopsy but not the ctDNA test.

The test was most sensitive for colorectal cancers, including early stage cancers. However, it was less sensitive for advanced precancerous lesions, which carry a risk that they can later become cancer.

“Colorectal cancer is common and very preventable with screening, but only about 50 percent to 60 percent of people who are eligible for screening actually take those tests,” said Grady, who is also the medical director of Fred Hutchinson’s Gastrointestinal Cancer Prevention Program. “Getting people to be screened for cancer works best when we offer them screening options and then let them choose what works best for them.”

Colorectal cancer is the second most common cause of cancer deaths in adults in the United States, according to the American Cancer Society. It’s expected to kill 53,000 people in 2024.

While colorectal cancer death rates have declined in older adults, rates among people under 55 have increased by about 1% a year since the mid-2000s.

People at average risk should begin screening at age 45, according to current guidelines.

“We continue to see younger people getting colorectal cancer and it’s now the third most common cancer for people under the age of 50,” said Grady. “Having a blood-based test for people to take during routine doctor’s visits could be an opportunity to help more people be screened.”

Dr. Jeremy Kortmansky, the clinical director of the GI Medical Oncology Division at Yale Cancer Center in Connecticut, told Medical News Today it’s difficult to get a higher accuracy rate in the home-based tests because the sensitivity of home-based stool tests correlates with the size of the polyp or cancer.

“A smaller lesion has less DNA shedding, limiting detection in the stool sample. As the size of the lesion increases, so too does the sensitivity of the assay,” explained Kortmansky, who was not involved in the new study.

Kortmansky acknowledged the difficulty in getting people to do the home-based test, which may have much to with why the rates are high.

“Although it is a home-based test, the volume of stool required is large and collection may be unpleasant; the so-called ‘yuck’ factor,” he said.

“Additionally, a prescription is required to obtain the test, so access to a healthcare provider is still necessary,” he added.

Dr. Anton Bilchik, a surgical oncologist as well as the chief of medicine and director of the Gastrointestinal and Hepatobiliary Program at Providence Saint John’s Cancer Institute in California, told Medical News Today he’s seeing a “rapid increase” in young people being diagnosed with colorectal cancer.

“One possible reason relates to the microbiome (bacteria in our body) and their effect on our immune system,” said Bilchik, who was not involved in the new study. “A disruption in the balance of the microbiome could be important in the development of colon cancer. This is a very important study because it describes that a subtype of the bacteria Fusobacterium (typically found in the mouth) may be responsible for tumor growth.

Bilchik said the study is important for other reasons, too.

“This information provides functional detail as to how it may be related to colorectal cancer,” he said. “The technology described in this study could also be used to evaluate other bacteria that may be helpful in preventing colorectal cancer.”

“This information may be important in both diagnosing colon cancer and potentially preventing it. Furthermore, it provides specific targets for future therapies,” he added.

Kortmansky said there are some indicators that people may have colorectal cancer.

“Symptoms of colon cancer can include abdominal pain or cramping, change in stool habits – more constipation or diarrhea – blood in the stool or weight loss. Low iron levels in the blood can also be a sign of cancer,” he said.

“The value of screening is to detect cancers or pre-cancers early, when they are not symptomatic and highly curable,” Kortmansky noted.