New home blood test detects colorectal cancer at an early stage

Researchers report that a new home blood test for colorectal cancer [1] is as accurate as current home tests using fecal stool samples.

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

Doctors say they hope such a new test will encourage more people to get tested for colorectal cancer early.

"The study results are a promising step toward creating more convenient tools for early detection of colorectal cancer when it is easier to treat," said Dr. William Grady, study author and gastroenterologist at the Fred Hutchinson Cancer Center in Seattle. "A test that has accuracy in detecting colorectal cancer comparable to blood tests used for early cancer detection may offer an alternative for patients who might otherwise forego current screening methods."

The new findings come from the ECLIPSE study ECLIPSE study, a multicenter clinical trial that analyzed test results from nearly 8,000 people between the ages of 45 and 84.

The ECLIPSE study compared the results of colonoscopies - currently considered the best way to detect colorectal cancer - with Guardant's Shield blood test.

The Shield test detects signals of colorectal cancer in tumor-derived blood DNA, which is called circulating tumor DNA (ctDNA). This measurement is also used in liquid biopsy tests used to monitor cancer recurrence in people who have already had cancer. It is also being used for other new cancer screening tests, the authors note.

Of the 7,861 people studied, 83% of participants with colon cancer confirmed by colonoscopy had a positive blood test for ctDNA, while 17% had a negative test. In the latter group, colorectal cancer was confirmed by biopsy but not by ctDNA test.

The test was most sensitive to colorectal cancer, including early stage cancers.

"Colorectal cancer is common and preventable through screening, but only about 50 to 60 percent of people who are appropriate for screening actually get those tests," said Grady, who is also medical director of the Fred Hutchinson Colon Cancer Prevention Program. "People's propensity to be screened is best shown when we offer them screening options and then let them choose what works best for them."
Although colorectal cancer deaths have declined in older adults, the death rate for those under 55 has increased by about 1 percent per year since the mid-2000s.

Current recommendations suggest that people at average risk should start screening at age 45 should start screening at age 45.

"We continue to see young people getting colorectal cancer, and it is now the third most common cancer among those under 50," Grady said. "Having a blood test to take during regular doctor visits may be an opportunity to help more people get screened."

Dr. Jeremy Kortmanski, clinical director of the Division of Medical Oncology at Wale LCDC in Connecticut, said it's difficult to achieve higher accuracy in home tests because the sensitivity of home blood tests correlates with the size of the neoplasm.

"A smaller defect has less DNA extraction, which limits detection in a fecal sample. As the size of the defect increases, the sensitivity of the assay also increases," explained Kortmanski, who was not involved in the new study.

"Symptoms of colorectal cancer may include abdominal pain or cramps, changes in defecation habits - more frequent 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 precancerous conditions early, when they show no symptoms and can be successfully treated," Kortmanski noted.