New Test Can Detect Colorectal Cancer, Polyps Without Invasive Screening


David Ahlquist, M.D.

 

DEAR MAYO CLINIC:

I recently read about a stool test that can detect colon cancer without a colonoscopy.

Is it just as effective as a colonoscopy, and if so, when will this be an option for everyone?

ANSWER:

The test you heard about detects colorectal cancer or precancerous polyps by measuring DNA in your stool.

This screening exam is noninvasive and requires no preparation or procedure. It appears to be highly effective at detecting colorectal cancer and precancerous polyps.

But more research needs to be done before the test is available to the public.

Currently, colorectal cancer screening often involves a colonoscopy to detect changes or abnormalities in the large intestine (colon) and rectum. During a colonoscopy, a long, flexible tube (colonoscope) is inserted into the rectum. A tiny video camera at the tip of the tube allows the doctor to view the inside of the entire colon.

Polyps or other types of abnormal tissue can be sampled or removed through the scope during a colonoscopy.

Understandably, many people worry about having a colonoscopy.

In addition to being an invasive procedure, a colonoscopy requires bowel preparation and sedation. The DNA stool test is non-invasive and a more patient-friendly screening option. No bowel preparation, diet change, or medication restriction is required.

For the DNA stool test, a patient simply provides a single stool sample, which is screened in a laboratory for evidence of colorectal cancer.

Colon cancers and polyps shed DNA that is passed in the patient's stool. In the lab, technicians can extract DNA from the stool. From that DNA, they can identify gene changes that suggest the presence of cancer or polyps.

While the DNA stool test has existed for some time, researchers at Mayo Clinic recently implemented several technical improvements to the test that have nearly doubled -- to about 90 percent -- the sensitivity of stool DNA testing for detecting colorectal cancer. Research also found that the stool test results did not differ by cancer stage; early-stage cancers were just as likely to be detected as late-stage cancers.

This is significant because if colorectal cancer is detected early in someone who has no symptoms, the large majority of those cancers are curable. Furthermore, the stool DNA test detected nearly 70 percent of premalignant polyps.

Detection and removal of such polyps can prevent colorectal cancer.

In addition, researchers demonstrated that the DNA stool test could detect common gastrointestinal cancers above the colon -- including pancreatic, stomach, biliary and esophageal cancers. Historically, cancer screening has been approached one organ at a time.

Stool DNA testing could shift the strategy of cancer screening to multiple organs, and open the door to early detection of cancers above the colon which are currently not screened.

More work is required to improve the test before it's a viable screening option for all.

Researchers hope that the next generation of DNA stool tests will have significant improvements in accuracy, processing speed, and affordability.

Next generation tests also are expected to have the capability of predicting the tumor site, which will help physicians direct diagnostic studies and minimize unnecessary procedures.

Although more research is needed to confirm the recent research findings and improve the test, the DNA stool test has the potential to become a widely used, cost-effective way to screen for colorectal cancer, and it could have a significant impact by reducing deaths from all gastrointestinal cancers.

-- David Ahlquist, M.D., Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minn.

Medical Edge from Mayo Clinic is an educational resource and doesn't replace regular medical care.

 

 

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