Early detection of colon cancer can prevent most deaths from this disease, perhaps up to 73 percent of them. But only 50 to 75 percent of older and middle-aged adults who should be screened regularly actually get screened.
Doctors say one reason is that screening methods discourage many patients.
People who are at average risk have two options: a colonoscopy every ten years or a stool test every one to three years, depending on the type of test.
Or, as Folasade P. May, a gastroenterologist at UCLA Health, puts it: “Either you take that horrible laxative and then a doctor inserts an instrument up your butt or you have to handle your own poop.”
But there is something much simpler on the horizon: a blood test. Gastroenterologists say these tests could eventually become part of the routine blood tests that doctors order when, for example, a patient comes in for their annual physical.
“I think this is going to start to become more common,” said John Carethers, a gastroenterologist and vice chancellor of health sciences at the University of California, San Diego campus.
About 53,000 Americans are estimated to die from colorectal cancer this year. It is the second most common cause of cancer-related death in the United States, and although the death rate has decreased in older adults, it has increased in people under 55 years of age.
Current guidelines recommend that people start screening at age 45. The problem is convincing more people to take the studies.
Now we have the blood test, which takes advantage of the discovery that both colon cancer and large polyps—clumps of cells that form in the lining of the colon and sometimes become cancer—shed off fragments of DNA that go to the blood.
A study published Wednesday in The New England Journal of Medicine revealed that a blood test that looks for that DNA called Shield and conducted by the company Guardant Health detected 87 percent of cancers that were in an early and curable phase. The false positive rate was ten percent.
“This is great news,” said May, who is a consultant for Exact Sciences, maker of Cologuard, the stool test.
But the blood test has a drawback: While it detects cancer, it misses most large polyps and only finds 13 percent of them. Instead, Carethers explained, stool analysis detects 43 percent and colonoscopy identifies 94 percent.
Although polyps are almost always harmless, some of them can turn into cancer, so doctors try to find and remove them to prevent it from developing.
Barbara Jung, chair of the department of Medicine at the University of Washington and president of the American Gastroenterological Association, said patients should have complete information before opting for the blood test. Above all, they have to understand that although the test helps detect cancer early, it does not prevent it because it is not used to find precancerous polyps.
“We need to talk about it” with patients, he added, “many of these issues will be the responsibility of primary care doctors, who are already under a lot of time pressure to go through a series of exams and consultations.”
Doctors should also explain to patients that if the blood test result is abnormal, they will need to schedule a colonoscopy to look for any early cancer or polyps and, if present, remove them.
It is also not known how often these blood tests should be done. Guardant recommended every three years, but that recommendation is not well founded, Jung explained.
Jung added that she would love to know if the blood test works for people who are too young to receive existing screening tests. But more studies will be needed to find out. Jung is concerned about rising rates of colon cancer in younger people. It would be “very nice” if patients in their 30s could have a blood test for colon cancer, he said.
“I would love that very much,” he said.
However, the big unknown is the cost. Guardant has already asked the Food and Drug Administration (FDA) for authorization to market the test. The company is currently selling it as a “lab test,” which does not require FDA approval, but health insurance does not cover it. For those who want to pay out of pocket, the price is $895, but if approved, the company will work with Medicare and Medicaid, as well as private insurers, to “set a final price,” said Matt Burns, a Guardant spokesperson.
William Grady, medical director of the gastrointestinal cancer prevention program at Fred Hutchinson Cancer Center, who is also the lead author on the Guardant-sponsored trial, said the company may set a price that is equivalent to the of other detection methods. The Cologuard stool test costs $581 to $681. Colonoscopies, which are typically required about half the time, typically cost between $1,250 and $4,800, although they are more expensive at some hospitals. The average cost of a colonoscopy in the United States is US$2,750 and health insurance most commonly covers this expense.
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