Experimental Colon Cancer Tests Pass FDA Panel Review
Article date: March 28, 2014
By Stacy Simon
Editor’s note August 12, 2014: The FDA has approved Cologuard, the first stool-based colon screening test that uses DNA to detect abnormalities. The American Cancer Society is studying the evidence to determine how it fits in with colon cancer screening recommendations.
A committee of the US Food and Drug Administration (FDA) has decided the benefits outweigh the risks of 2 experimental tests that look for certain DNA changes (mutations) in cells that can cause colon cancer. The FDA does not have to go along with the recommendations from its advisory panel, but usually does. The American Cancer Society will review all the data on the new tests and decide how they may or may not fit in with current guidelines for colon cancer testing.
One of the tests, Epi proColon developed by the German company Epigenomics, is a blood test that looks for DNA changes that can indicate cancer. The other test, Cologuard, made by the Wisconson-based company Exact Sciences, is a stool test that can find abnormalities that indicate cancer or pre-cancerous growths (polyps). The patient uses a kit at home to collect a stool sample and mail it to a lab for analysis. The test checks for the presence of blood in the stool that can indicate cancer or pre-cancerous polyps, and also checks for DNA changes that could indicate cancer. If either the Epi proColon test or the Cologuard test does indicate cancer, the patient would then need a colonoscopy to confirm it. Neither test is currently available in the US outside of clinical trials.
The FDA committee based its approval of the Cologuard test on a study of almost 10,000 people ages 50 – 84 years at 90 sites in the US and Canada. The participants had no symptoms of colon cancer and were considered to be at average risk. Each participant was screened with the Cologuard test, the fecal immunochemical test (FIT), and a colonoscopy. Colonoscopies confirmed that 65 of the participants had colon cancer and 757 had advanced pre-cancerous polyps. The Cologuard test detected significantly more of the colon cancers (92.3%) than FIT (73.8%), and it found significantly more of the polyps (42.4% vs. 23.8%). The Cologuard test, however, also had a higher number of false positives. The study was published online March 19 in the New England Journal of Medicine.
In approving the Epi proColon test, the FDA committee discussed 2 clinical studies that compared the test to FIT and colonoscopy. Several committee members did express some concern about a high number of false positive results, which means the test found cancer when cancer was not present.
The importance of colon cancer screening
Colon cancer rates have dropped 30% in the past 10 years in people 50 and older, which is thought to be the result of increases in screening. Screening, the process of looking for cancer or pre-cancer in people who have no symptoms of the disease, can find colon cancer early, when it’s easier to treat. Screening can also sometimes find polyps so they can be removed before they turn into cancer. However, colon cancer is still the third most commonly diagnosed cancer and the third leading cause of cancer death in both men and women in the US. In 2010, only 59% of people ages 50 or older, the population most at risk for colon cancer, reported being up to date with screening.
The tests currently available to screen for colon cancer can be divided into 2 groups – those that can find both polyps and cancer, and those that mainly find cancer. Those that can find both polyps and cancer – (colonoscopy, CT colonography (also called virtual colonoscopy), and double-contrast barium enema – require a bowel prep that is unpleasant for many people and may discourage them from getting screened. The prep may include eating a special diet, drinking up to a gallon of a liquid laxative, and sometimes enemas to clean out the colon.
The available tests that mainly find cancer, the fecal occult blood test (FOBT) and FIT, examine the stool to look for signs of cancer. People take these tests at home with a kit they receive from their doctor’s office, along with instructions. The tests do not require a bowel prep. Developers of the Epi proColon and Cologuard tests say they may encourage more people to get screened because they offer more choices of tests that are non-invasive and don’t require a bowel prep.
Citation: Multitargeted Stool DNA Testing for Colorectal-Cancer Screening. Published March 19, 2014 in the New England Journal of Medicine. First author Thomas F. Imperiale, MD, Indiana University, Indianapolis.
Reviewed by: Members of the ACS Medical Content Staff
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