By CARLA K. JOHNSON (AP Medical Writer)
A blood test for colon cancer did well in a research released on Wednesday, offering a new type of screening for a leading cause of cancer deaths.
The test searches for DNA fragments released by tumor cells and precancerous growths. It is currently available for purchase in the U.S. for $895, but has not been approved by the Food and Drug Administration and most insurers do not cover it. The maker of the test, Guardant Health, expects an FDA decision this year.
In the research, the test detected 83% of the cancers but few of the precancerous growths identified by colonoscopy, the gold standard for colon cancer screening. Besides identifying tumors, colonoscopies can prevent the disease by removing precancerous growths called polyps.
However, some people avoid the exam due to the inconvenience of taking time off work or the day-ahead preparation involving drinking a strong laxative to empty the bowels.
A convenient option is an annual stool test, where people send a stool sample to a lab for analysis.
“The best test is the one someone will actually complete,” said Dr. Douglas Corley, chief research officer for Kaiser Permanente, Northern California, who was not involved in the study. “Giving people a choice increases the number of people who will get screened.”
In the U.S., screening is recommended for healthy adults ages 45 to 75 at average risk for colon cancer. The frequency depends on the test: a routine colonoscopy is every 10 years. Screening is increasing but falls short of the 80% of age-eligible adults goal set by the American Cancer Society and other groups.
Guardant recommends testing with its blood test called Shield every three years. Like a stool test, the blood test requires a follow-up colonoscopy if there’s an abnormal result, which could lead to more out-of-pocket costs.
The research, funded by Guardant and published in the New England Journal of Medicine, involved 7,861 people in the U.S. who had both a colonoscopy and a blood test.
Although the blood test identified 83% of the cancers found by colonoscopy, it missed 17%. This is similar to stool-based tests.
There were also false alarms: For 10% of the people where the colonoscopy found nothing, the blood test falsely indicated they might have colon cancer. That means a significant number of people would face the anxiety of follow-up colonoscopies.
The blood test is designed to detect the signature of colon cancer, but more research is needed to determine if it might also detect other cancers and give inaccurate results, Corley said.
Colorectal cancer is the second leading cause of cancer deaths in the United States and the third worldwide. In the U.S., more than 153,000 new cases and 53,000 deaths from the disease are expected this year.
Increased screening should lead to fewer cancer deaths, said study co-author Dr. William Grady of the Fred Hutchinson Cancer Center in Seattle and a paid member of Guardant’s scientific advisory board.
In a separate research published on Wednesday in the same journal, an updated version of the Cologuard stool test, which also looks for DNA fragments, appeared to improve its performance on false alarms, possibly resulting in fewer follow-up colonoscopies. That study, involving over 20,000 people, was funded by Exact Sciences, the maker of the test.
Dr. Nabil Mansour from Baylor College of Medicine, who was not part of the studies, said that having more options for patients is beneficial. He will still suggest a colonoscopy for his patients but is enthusiastic about the availability of a reliable blood test option.
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The Associated Press Health and Science Department is supported by the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.
