New test possible aid to overcoming barriers to colon cancer screening

A new option for non-invasive colorectal cancer testing may encourage some people who avoid screening for the deadly disease to be tested.

A study published in the December 23 issue of the New England Journal of Medicine reports that a non-invasive test for DNA mutations present in stool has an encouraging rate of detecting colorectal cancer compared to the standard non-invasive method — fecal occult (hidden) blood stool testing, although neither approached the detection rate of colonoscopy, an invasive procedure.

“A simple, non-invasive test that detects tumor-specific products with reasonable sensitivity and specificity might overcome barriers to screening among persons who are not willing to have a more invasive test, such as colonoscopy,” said Thomas Imperiale, M.D., professor of medicine at the Indiana University School of Medicine and a research scientist at the Regenstrief Institute.

The study, conducted at 81 sites by Dr. Imperiale and colleagues of the Colorectal Cancer Study Group, reports that in average risk, asymptomatic individuals the fecal occult blood test — which tests blood hidden in stool — found only 13 percent of colorectal cancer; while the new stool DNA test detected 52 percent of the cancers. Colonoscopy, which is presumed to find all colon cancers, is the “gold standard” against which all other tests are measured.

Typically, colorectal cancer develops slowly over a period of several years, usually beginning as a growth of tissue known as a polyp that develops on the lining of the colon or rectum. Most cancerous lesions bleed intermittently, however many precancerous polyps do not bleed. Absence of fecal occult blood cannot rule out cancer or precancerous lesions.

Previous studies have found that polyps as well as cancerous lesions may shed abnormal DNA. It is this DNA which the stool DNA panel analyzes. Although researchers found that the majority of precancerous polyps discovered during colonoscopy were not detected by either non-invasive test, they report that the stool DNA panel detected a greater proportion than did analysis of stool blood.

Despite national guidelines recommending screening, fewer than half of American adults aged 50 years and older have had a recent examination for colorectal cancer at the proper interval according to Centers for Disease Control. “There are many reasons why people don’t get screened for colon cancer,” said Dr. Imperiale. “Some individuals do not want colonoscopy because of discomfort despite conscious sedation, its inconvenience, or its risk for complications; others are unwilling to smear stool samples on a card for the occult blood test every year.” The stool DNA panel test, which requires a single sample expelled from the body directly into a container, gives people who are not getting screened with any of the currently available methods, another noninvasive option.

According to the American Cancer Society colon cancer is the third leading cause of cancer death among men and women in the United States.