Tell colonoscopy patients their cancer could be missed: Bushell lecture

People who undergo a colonoscopy should be informed there is a small chance their cancer could be missed, an international expert says.

Delivering the Bushell Lecture on colonoscopy effectiveness and lessons for the real world Dr Linda Rabeneck, Vice President of the Prevention and Cancer Control at the Cancer Center in Ontario said patients should be informed of the risk the same time they are warned about the risks of bleeding and perforation associated with the procedure.

This was because it was now well established, and accepted, that in usual practice colonoscopy was less effective for the proximal colon, Dr Rabeneck explained.

A study conduced at her institution nearly 10 years ago involving over 12,000 people with a new diagnosis of colorectal cancer found that the rate of new or missed cancers was two to six percent.

Factors associated with increased risk of a missed cancer were increased age, the presence of diverticular disease, right-sided colon cancer, having a procedure performed by someone other than a gastroenterologist or surgeon and having a non-hospital based colonoscopy.

“The main point here is there is a risk of new or missed cancers and factors associated with this is the cancer is right-sided,” she told delegates.

Another case controlled study looking at the effectiveness of colonoscopy in over 10,000 people with a new diagnosis of disease and 50,000 matched controls revealed a 40 percent reduced risk of death from bowel cancer for people who had a prior colonoscopy compared to people who didn’t.

But when the researchers separated the cancer deaths into those who died from left- sided disease and those who died from right-sided disease they found the Odds Ratio for right-sided colon cancer wasn’t significantly different from 1.

They concluded that most of the reduction in death from having a prior colonoscopy was related to the marked reduction in death from left-sided disease.

“Was this a surprise? Absolutely! But that’s what we found in Ontario for that time period,” she told delegates.

At the time the study caused quite a hulabaloo and even became the subject of an editorial in the New York Times titled Not perfect, Still essential.

“There have been occasional disquieting reports that doctors may miss polyps or cancers that they should have seen. Now a large study in Canada, published recently in the Annals of Internal Medicine, makes that conclusion hard to escape” the article stated.

“I think that really nailed it… it makes that conclusion hard to escape,” Dr Rabeneck reminisced.

Nonetheless, subsequent studies have borne this out,” she said.

“The big question is, is this an issue of the quality of our procedures or the biology of the disease itself?” she asked.

Potential scenarios were that the cancer was either not seen, not completely removed or not there at the time.

“In our practice we all know to tell patients about the risk of bleeding or perforation,” she told the packed room.

“But now we know that if the patient has a cancer there’s a small chance we might miss it so we think it is important to tell patients” she said.

She advised adding the statement to the standard informed consent statement around bleeding and perforation risk.

And while bowel prep was important too, it was also really important to have a very careful standard colonoscopy technique, she added.

“A lot of emphasis has been put on these advanced techniques but I think a careful standard technique is the most important thing we can do right now.”

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