Laxative-free cancer scans nearly as effective as colonoscopies

Posted May 15, 2012, at 9:12 a.m.

NEW YORK — Colon cancer screenings that don’t require laxatives are almost as effective as colonoscopies and may encourage more people to be tested, researchers said in a study published Monday.

Computed tomography, or CT scans that add a contrast agent to identify fecal material in the colon, found polyps at a size most likely to turn cancerous in 91 percent of patients, according to a study published Monday in the Annals of Internal Medicine. That compares with 95 percent of patients identified using standard colonoscopy, which involves clearing with laxatives and then inserting a tiny camera into the bowel.

People are reluctant to have the procedure because they have to spend the day before taking laxatives to clear out the bowels to remove feces that may interfere with seeing lesions. The results suggest a less-invasive approach may work just as well, although more studies are needed, the researchers said.

“Rightly or wrongly, people really do harbor a strong aversion to the prep,” said Michael Zalis, director of CT Colonography at Massachusetts General Hospital in Boston and an associate professor of radiology at Harvard Medical School, in a telephone interview. “To the degree that we can make something easier for them, that’s an important step. Nobody should be dying of colon cancer. The key is getting people involved in screening,”

General Electric Co., the world’s biggest maker of medical imaging equipment, and the American Cancer Society funded the study.

More than 103,000 new cases of colon cancer will be diagnosed this year and about 50,000 people die of the disease in the United States, according to the National Cancer Institute. Many of the deaths could be prevented by screening, said Zalis, the study’s lead author.

The study included 605 adults ages 50 to 85 years who were at average to moderate risk for colon cancer. Patients first underwent CT-scan colon screenings with contrast and then the more-common optical colonoscopy with laxatives.

To prepare for the CT scan screening, patients ate a low- fiber diet for two days before the procedure and ingested small doses of a contrast agent to help identify the fecal material in the intestine. Software programs developed by the researchers were able to take out the labeled feces to analyze the images for lesions.

Patients then also underwent a standard colonoscopy, which involved taking a laxative with as much as a gallon of liquid the day before the procedure. During a colonoscopy, patients are sedated while a fiberoptic tube with a camera and light are inserted into the intestine. Patients also completed questionnaires about the procedures.

The researchers found that the CT scan screening detected 20 out of 22 confirmed lesions that were 10 millimeters or greater in size, which are most likely to become cancerous, Zalis said. The optical colonoscopy found 21 out of the 22, he said. During the study there were three cases of colon cancer diagnosed among the patients, all detected by both screening types.

CT scan with contrast wasn’t as good at finding smaller polyps, the study showed. The laxative-free test found 59 percent of lesions 6 millimeters or bigger, while the laxative test identified 76 percent, Zalis said.

The false-positive rate for the laxative-free scan for polyps 10 millimeters and larger was 15 percent compared with 11 percent for colonoscopy, the study showed.

Douglas Rex, a professor of medicine at Indiana University School of Medicine in Indianapolis, who wasn’t involved in the study but researches colon cancer screenings, said a procedure that’s unable to identify smaller polyps won’t be a tool that experts would consider good enough to use on patients. He said many patients want polyps that are six millimeters and larger removed.

“The results of this study indicate that patients are better off having a colonoscopy and only choosing a study like CTC if they can’t tolerate or refuse the prep,” he said in an email. “The advantages of screening colonoscopy are worth the inconvenience of the bowel preparation. This test is an alternative if you can’t tolerate the preparation but the results are not as reliable as colonoscopy and commonly lead to unnecessary colonoscopy to find a lesion that isn’t really there.”

He said a head-to-head study comparing CT scan colonography to optical colonoscopy in the U.S. would be useful.

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