New laxative-free colonoscopy shows promise

Tuesday, May 15, 2012 - 7:42am

If you're turning 50 or you're already there, colorectal screening is in your future. Although you would only have to be screened every 10 years (if no polyps are found), the prospect of getting prepped for procedure is a big turn-off for many. You've probably heard some of the horror stories about the pre-screening laxatives, the taste, the amount, the ensuing "cleansing."

But for those who are a little squeamish about all that liquid going in--and coming out, a new laxative free colonoscopy might be on the horizon. A study of 605 adults published Monday in the Annals of Internal Medicine shows this type of colonoscopy has promise.

This new exam is called a laxative-free computed tomographic colonography (CTC) or virtual colonoscopy. Study author Dr. Michael Zalis, Director of CT Colonography at Massachusetts General Hospital says the hope is that more people will find this preparation easier to stomach and result in more people getting this life-saving test.

"When we do a virtual colonoscopy we give a safe contrast agent that patients ingest over 2 days with snacks," Zalis said. "It's about 5 milliliters, about the volume of food you would see in a ketchup packet."

The contrast is taken orally 1-3 times a day, mixes easily with a low-fiber diet a patient is consuming and shows up on an x-ray. The feces are tagged and have a distinctive appearance on the cat scan. The contrast is not absorbed by polyps or the colon wall. Researchers have developed computer software that cleanses the colon images electronically.

"We observed with this laxative-free version we could identify patients who had one or more polyps 1 centimeter or greater in size and we could do that with a performance that was very similar to optical colonoscopy and in a range that many people would consider acceptable for screening. We could detect 91% of these larger lesions, in our study, OC detected 95%. In this study that's the difference of 1 polyp."

Currently there are 2 main types of colon screenings, says Zalis: The regular optical and the virtual colonoscopies. For the optical colonoscopy (OC), a gastroenterologist inserts a 6-foot long scope with a camera at the end into the colon. This allows the doctor to see any polyps (pre-cancerous tumors) and immediately remove. The patient sedated for the entire procedure, so they shouldn't feel a thing. To prepare for this procedure, patients usually have to drink a laxative solution on the day before. This means they are drinking anywhere between 2 quarts and a gallon of liquid until the bowels are empty.

The computed tomographic colonography (CTC), sometimes called a virtual colonoscopy, requires the same preparation, it's the test that's different. A tiny tube the size of a pinkie is inserted. This screening uses a low-dose x-ray cat-scan instead of a scope that takes pictures of the colon that are fed into a computer and later read by a technician, after the patient has left the exam. If polyps are found, the patient has to come back and have a regular colonoscopy to have the precancerous lesions removed.

"They both require a full laxative prep and the prep is found to be so unpleasant that it deters people from participating in screening," Zalis said. "Nobody should be dying of colon cancer. It's a slow-growing disease."

And largely preventable. Polyps are not cancerous, but they are a benign precursor that can turn into cancer if left unchecked. According to the American Cancer Society, colon cancer deaths has been dropping over the last 2 decades. Still, there are about 104,000 new cases of colon cancer each year and approximately 51,000 deaths.

There is a caveat when using this new type of "cleanse" - while the laxative-free test accurately detected polyps 1 centimeter (0.4 inches) and larger during the study, it was less successful finding smaller growths. But Zalis says smaller lesions are clinically less important. "We can't ignore them, but we know that the most important lesions to get are the advanced adenomas and 90% of them are 1 centimeter or larger."

Researchers say results from this study need to be validated by another larger study. In the meantime, Zalis is making this test available to his patients at Mass General, even though it is not yet fully covered by Medicare or insurance. The cost for this test is not higher than a traditional virtual colonoscopy, Zalis says, because the method of cleansing the bowel is all that changes.

"We've known for a long time if we could make and validate a colon exam that was far more patient-friendly, then we might be able to bring the benefit of screening to many people who are not participating in screening and who are at risk for colon cancer, " Zalis says.

A second colon cancer study also releasing in Annals looked at whether having an immediate family member such as parents, siblings and children with adenomatous polyps (larger polyps that can turn into cancer over time) increased a person's risk of colon cancer.

Researchers looked at 12 different studies and concluded that more studies are needed before a conclusion can be made.
 

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