Wednesday, 19 Mar 2014 08:26 AM
A novel colon cancer test from Exact Sciences Corp. (EXAS) and the Mayo Clinic using the DNA of specimens that patients collect at home detects more tumors than methods focusing on blood in the stool, a study found.
The research released Tuesday by the New England Journal of Medicine shows the test is about as powerful as a colonoscopy for spotting colon cancer, the third-most common type of tumor. While the disease can be prevented by identifying and removing abnormal growths early, as many as one-third of Americans haven’t taken the recommended screening to find them.
The test called Cologuard scans for traces of tumor DNA, genetic mutations and blood in a stool sample. It detected 92 percent of cancers and 42 percent of advanced precancerous growths, significantly more than an older test that looks only for blood in the stool. False positives occurred in more patients, about 13 percent, with Cologuard, leading them to undergo a colonoscopy that turned up no signs of cancer.
“It really is a more sensitive noninvasive screening test for colon cancer,” said Thomas Imperiale, a study author and professor of medicine at Indiana University Medical Center in Indianapolis. “It’s ready to be used right now, or very soon once it becomes widely available, but we also need additional data.”
It’s not clear how often the test should be given, Imperiale said in a telephone interview. That information, plus the price of the screening, is needed to determine how cost-effective it will be, he said.
More than 100,000 Americans are diagnosed each year with colon cancer, and 50,000 die from the disease, according to the National Cancer Institute.
Advisory Panel
Exact Sciences, based in Madison, Wisconsin, released the preliminary results of the study in April 2013. The company filed for U.S. Food and Drug Administration approval of the test in June and an advisory panel is scheduled March 27 to discuss the application.
The company’s shares gained 9.8 percent to $14.42 at the close yesterday in New York after a press statement with some study results was released by the Rochester, Minnesota-based Mayo Clinic on its website.
The study funded by Exact Sciences involved 9,989 patients who were screened with Cologuard, an older test for blood in the stool and a colonoscopy. Offering patients more choices may boost the number of Americans who are screened each year, the researchers said. A noninvasive test like Cologuard may appeal to people because of its high sensitivity for curable-stage cancer, they said.
Best Method
Colonoscopy is the most-effective available screening method for colon cancer, able to detect tumors or suspicious growths and treat them at the same time. It spots one case of cancer in every 154 people tested. The Exact Sciences product finds 1 in 166 people tested, while the older stool tests find 1 in 208 people.
People with results that indicate cancer or an abnormal growth with the stool tests must then undergo a colonoscopy. The stool tests avoid the special diet, preparation to clear out the bowel and the invasive procedure for people who are found not to show any signs of suspicious growths.
The test’s tumor-detection abilities were greatest for the earliest and most curable stages of colon cancer, with a 94 percent detection rate in those with stage I or II disease, the study found. Those levels haven’t been found with any other noninvasive test, said David Ahlquist, a gastroenterologist at the Mayo Clinic and a co-inventor of the test.
Finding Cancer
“It is our hope that this accurate and user-friendly test will expand screening effectiveness and help curb colorectal cancer rates in much the same way as regular screening, including genetic testing, has done for cervical cancer,” he said in a statement.
The development of DNA-based screening of stool for colon cancer has come a long way, reporting markedly higher cancer detection rates that earlier efforts, wrote Douglas Robertson and Jason Dominitz in an editorial that accompanied the study. The number of samples that couldn’t be used, at 689, was higher in the Cologuard group. It’s also unlikely that Cologuard would be done annually the way the older screening is used because of cost and false positives, they said, making it hard to compare the two approaches. The study only ran the screening tests once.
“There is also the issue of heightened concern when a patient is found to have a positive stool DNA test but a negative result on colonoscopy,” said Robertson, from Dartmouth College’s Geisel School of Medicine in Hanover, New Hampshire, and Dominitz, from the University of Washington School of Medicine in Seattle. “It is possible that some clinicians will choose to perform either earlier repeat colonoscopy or embark on further extracolonic workup for cancer in such patients.”