The guidance suggests cervical cancer screening should begin at age 25 and continue until age 69, at three year intervals. For years, women were advised to get an annual Pap smear, though in recent years a number of countries have lengthened the intervals between tests.
The guidelines are issued by the Canadian Task Force on Preventive Health Care, a federally funded group that advises doctors on what should be part of routine preventive care for their patients. The recommendations were drawn up for the task force by a working group that analyzed the medical literature to determine the best approach.
"Every three years will do the job. Doing it every year doesn't really add very much (protection) but it adds a lot of inconvenience and some harm," said Dr. James Dickinson, who chaired the working group and is a professor of family medicine at the University of Calgary.
The guidelines were published Monday in the Canadian Medical Association Journal.
In the decades since doctors began to look for pre-cancerous cells on the cervix using a test devised by Greek doctor Georgios Papanicolaou, rates of invasive cervical cancer and deaths to the disease have plummeted. The Canadian Cancer Society estimated that in 2012, 1,350 Canadian women were diagnosed with cervical cancer and 390 died from the disease.
The evidence shows that most of the gains from cervical cancer screening occur for women in their 40s and older, the point at which most cervical cancer cases are diagnosed.
But in younger women, abnormal test results are not uncommon, because the test picks up lesions caused by infections with the human papillomaviruses (HPV), which can cause cervical cancer.
Many of those lesions would heal on their own and would not go on to become cancer. But once they are found, women often have to undergo additional testing and treatments, some of which can make it hard for a woman to carry a pregnancy to term later.
Given these potential harms and the lack of evidence to suggest that screening offers any benefits to women under 20, the task force said doctors should not screen that population. They also said there is little evidence to support screening for women aged 20 to 24, and recommended against it as well.
The strongest evidence of benefit is in women aged 30 to 69, and they should be regularly screened, the recommendations said. In women aged 25 to 29, the benefits are less pronounced, but at that point they start to overtake the risks, and so the task force chose to recommend screening for that age group too.
Women 70 and older don't need to be screened if they have had three successive negative tests before they stop, the guidelines say.
Dr. Eduardo Franco, a cervical cancer expert at McGill University in Montreal, was involved in developing U.S. screening guidelines that were updated last year. Those guidelines recommended screening for women between the ages of 21 and 65. Franco said he feels that women who have had negative tests can safely stop cervical cancer screening at age 65.
He was pleased, however, that the Canadian guidelines moved to a testing interval of three years, calling it welcome news.
Dr. Joan Murphy headed a committee which last year updated Ontario's cervical cancer screening guidelines. That group recommended screening for women aged 21 to 70 — though it said women who are not sexually active by age 21 could wait until they become sexually active.
Murphy said she isn't concerned by these slight differences between the Ontario and national guidelines.
"I think for consumers, whether they be health-care professionals or the public, it's always easier when things are concordant. So there is an unfortunate element. But it's not a disaster," she said. Neither Murphy nor Franco were involved in crafting the national guidance.
She did admit, though, that a number of doctors are worried about moving away from the paradigm of annual Pap tests, because they fear women may forget to be screened at the prescribed interval.
"Yeah, there's tremendous concern about that," said Murphy, an associate professor of medicine at the University of Toronto. She said Cancer Care Ontario, the agency that oversees Ontario's cancer screening and treatment programs, is working to develop a reminder system that would fire off letters to all women due to be screened in a particular year.
Dickinson acknowledged the new interval will take some getting used to. But he suggested women might adopt a system where they book a Pap test in any year where their age was divisible by three.
One facet of the new recommendations is drawing some criticism. The national guidelines do not recommend use at this point of a new type of test for cervical cancer, one that looks for genetic material of the HPV viruses known to cause cervical cancer. The task force statement says there isn't enough data yet on these tests to warrant replacing Pap tests with HPV tests.
Franco said he was disappointed by that conservative approach; he believes there is good evidence to use the newer, more sensitive tests.
So does Cancer Care Ontario. The new Ontario guidelines call for HPV tests to be the primary test used; a positive HPV test would be followed up by a Pap test for confirmation.
But Murphy admitted the Ontario government hasn't yet approved the funds that would be needed to make the switch. Once HPV testing is adopted, she said, the interval between tests will be stretched out to every five years.
Both Dickinson and Murphy stressed the point that the move to lengthening the time between cervical cancer screening tests isn't about saving money, it's about not putting women through tests they don't need.
"We didn't consider such issues at all in our evaluations. We don't have any economic analyses because . . . that wasn't our purpose. We were just looking at: What is the value for women?" Dickinson said.
"We want to right-size it," Murphy agreed.
"There's a commonly held view out there that more care is better care. And that's not true. At all."
Note to readers: This is a corrected story. A previous version said Ontario recommends women start screening at 25. In fact, the recommended age is 21.
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