A New Way to Detect Colon Cancer
An at-home test makes screening more accessible
A new at-home test for colon cancer helps remove barriers to screening for this dangerous disease.
Approved by the Food and Drug Administration in August, the test has been available over-the-counter for those willing to pay its $599 price tag. This week, the Mayo Clinic made it available via prescription with Medicare reimbursement.
The test looks at DNA in stool to detect the presence of problematic tissue.
Only about half of people who should be getting screened for colon cancer currently follow the recommended screening protocol, says Harold Sox, emeritus chair of medicine at Dartmouth and former head of the U.S. Preventative Services Task Force.
Why so little compliance? One reason: the gold standard for colon cancer screening — colonoscopy — is expensive and inconvenient, involving an uncomfortable preparation period, sedation and the possibility of complications. Stool blood samples are also used as a colon cancer screen, and, while convenient and inexpensive, they are much less effective in detecting problems.
The new DNA test is relatively inexpensive and much more convenient than colonoscopy, which could help boost participation in these important screening protocols. And though in studies it didn’t catch as many cancers and precancerous areas as colonoscopy, it caught significantly more than did stool blood tests.
Colon Cancer Screening Options
Colon cancer is somewhat unique, says Sox, in that you can trace the development of benign tissue as it turns into something more problematic – and the best screening tests, such as colonoscopy, are effective because they can detect these cellular changes before they become full-blown cancers.
During colonoscopy, doctors push a camera on flexible tubing through the colon, allowing them to visualize the walls of the colon in real time and identify and biopsy any areas that seem cancerous or precancerous.
Stool blood tests analyze blood in the stool to detect the presence of tumors. This test is less sensitive than colonoscopy in detecting precancerous lesions.
The new at-home DNA test aims to identify both cancer and precancerous lesions in the colon by looking at DNA that has been shed in the stool.
When a cell “gets one mutation, that changes its characteristics,” says Sox. “Then a second mutation changes it more, and then eventually you pile up those mutations and those allow the cells to actually invade tissues where they don’t belong.”
In other words, as mutations in a cell add up, the cell moves from precancerous tissue to cancer.
“One of the nice things behind this new DNA test is that cells that may turn into cancer will often have the mutations and you can detect them by the DNA that is sloughed off through the surface of the colon,” says Sox.
The test, developed by a doctor at the Mayo Clinic, costs $599 and is easy to use. People who order the test collect a stool sample at home and then mail it to a lab for analysis.
Stool blood tests cost around $25, and colonoscopies cost upwards of $1,000.
Which Screening is Best?
In a study published in the New England Journal of Medicine in April, researchers compared stool blood tests and the new DNA tests in their ability to identify cancer and precancerous cells. The study looked at 9,989 participants, 757 of whom had cancer or precancerous lesions that had been identified with colonoscopy.
The DNA tests had a 92.3 percent sensitivity rate for detecting colorectal cancer. The blood tests identified 73.8 percent of colon cancers.
When it came to identifying precancerous lesions, the DNA test did not perform as well as it did when pinpointing full-blown cancer, but it significantly outperformed the blood test: DNA analysis caught 42.4 percent of precancerous lesions and the blood test caught 23.8 percent.
So the test, says Sox, is not as good as colonoscopy. But it is also not bad.
The main takeaway, stresses Sox, is that screening is critical.
“It is one of the top two or three cancers in terms of number of deaths caused and frequency itself,” says Sox. “It is a big deal.”
The U.S. Preventative Services Task Force recommends that adults ages 50 to 75 with no increased risk of colon cancer should follow one of three screening protocols:
- Annual stool blood tests
- A sigmoidoscopy (which is a less involved, though a correspondingly less comprehensive, form of colonosocopy) every five years plus stool tests every three years
- A colonoscopy every decade