Colorectal cancer screening may not be best for all, new guideline says

Routinely screening everyone aged 50 to 79 for colorectal cancer may not be the best approach, a panel of Canadian and international experts say.

Colorectal cancer is the most commonly diagnosed cancer in Canada affecting about 25,000 a year. It is the second leading cause of cancer death in Canada in men, and the third leading cause of death in women.

Currently, Canadian gastroenterology guidelines call for screening to begin at age 50 for those without a diagnosed parent, child or sibling. 

Dr. Gordon Guyatt, professor of medicine at McMaster University in Hamilton, chaired a panel to review the latest evidence on screening to reduce the risk of developing or dying of colorectal cancer by removing precancerous growths called polyps.

Most guidelines recommend starting screening at age 50. At that point, the risk of developing colorectal cancer over the next 15 years is about one to two per cent.

"We ended up suggesting … if your risk is over three per cent, perhaps not a bad idea to go through screening," Guyatt said. "If it's under three per cent then for you the benefits might not be worth the harms and burdens."

As a result, the new guideline says those at lower than average risk may favour holding off on screening. 

Individualized approach

In Wednesday's issue of BMJ, the panel suggested individuals turn to an online calculator called Magicapp. Users can plug in their age, sex, family history of colorectal cancer, body mass index, smoking status, ethnicity and other information to estimate your risk of developing colorectal cancer in the next 15 years.

Dr. Linda Rabeneck, vice president of prevention and cancer control at Cancer Care Ontario, said the panel called for a more individualized approach to colorectal screening to help people make an informed decision.

"It's fair to say that's not what we're doing today in colorectal cancer screening in general not just in Canada but beyond if you look in Europe and so forth," Rabeneck said.

The gastroenterologist said everyone over 50 is invited to screening. Then the interval between screens stays the same even though the risk increases with age.

But the cancer field is moving away from taking a blanket approach to the whole population and refining it to consider an individual's risk.

"On balance I think that this is something we need to think hard about," she said.

Dr. Desmond Leddin, an adjunct professor in gastroenterology at Dalhousie University in Halifax, said he would not change current practice based on the new guideline. He has another priority.

"All Canadians should have access to a family doctor since in our system they are gatekeepers to care," Leddin said in an email.

"I agree with the authors that the risks and benefits of screening should be weighed up and that is best done in a conversation with a family doctor. Many people do not have a family doctor and some provinces send the screening test directly to the patient."

'Seismic shift'

The researchers had gold-standard randomized control trial data on tens of thousands to compare sigmoidoscopy, a scope of the lower part of the colon, to no screening to draw on for their review.

But for newer screening with an at-home fecal test called fecal immunochemical test (FIT) and colonoscopy of the entire organ, the trials aren't yet complete. Instead, the authors used models filled with assumptions, Rabeneck said.

A journal editorial published with the study called the move away from organized screening and towards informed choice a "seismic shift."

Philippe Autier at the International Prevention Research Institute in Lyon, France, wrote that the objective of public health policies is to persuade people to attend screening and to maximize uptake. Screening messages tend to overstate benefits and downplay potential consequences.

In contrast, the individualized approach "is increasingly regarded as the most appropriate way to discuss cancer screening," Autier said.