In most Canadian provinces, women are told to visit a health-care provider every three years to get a Pap test to check for cervical cancer.
But a new study published last week in the Journal of the American Medical Association suggests that women are getting the wrong test: as a first step, they should be tested for the human papillomavirus instead.
The randomized clinical trial, which examined more than 19,000 women in B.C., found that the HPV tests detect potentially cancer-causing lesions sooner and more accurately than Pap tests. After 48 months, fewer women who had taken the HPV test had pre-cancerous lesions than women who had taken a Pap test.
“What we found was using HPV, we were able to detect those pre-cancerous lesions earlier,” said Dr. Gina Ogilvie, one of the study authors and a professor in the faculty of medicine at UBC.
Early detection matters because cervical cancer can often be prevented – treatments to destroy or remove pre-cancerous cells can stop the disease from turning into full-blown cancer.
The study’s second major finding was that if an HPV test was negative, meaning the woman didn’t have HPV, they were less likely to have signs of cervical cancer four years later, when compared to the Pap test group.
“If you were HPV negative, you had more confidence in that negative result because four years later, you were much less likely to have any precancerous lesions compared to women who were cytology negative,” said Ogilvie.
About 99.7 per cent of cervical cancer cases are caused by an HPV infection, particularly one that lingers. “So when we learn that, this then starts to make sense. Let’s look for the virus that causes the persistent infection that goes on to cause precancerous lesions that then go on to cause cancer.”
Changing testing programs
Dr. Joan Murphy, clinical lead of the Ontario Cervical Screening Program, said that evidence has been building for years in favour of HPV testing as the primary test to screen for cervical cancer.
“HPV is more reliable in the sense that if HPV is present, it will be detected almost always. So a negative test is very reliable — it tells us the woman is not at risk.” A positive result means that the woman should have a follow-up test to determine if there needs to be a medical intervention, or if she should just be observed more closely as many HPV infections dissipate on their own without much harm.
HPV is very common — Health Canada estimates that about 70 per cent of sexually-active adults will develop it at some point in their lives. But not every case leads to cancer.
“It’s very common and like the common cold, it comes and goes and often causes no trouble.”
Cancer Care Ontario recommends that HPV tests should be used as the first test, and the Ontario government promised in its 2017 budget to change the screening system to do HPV testing first. No Canadian province currently does this, said Murphy, and Ontario hasn’t implemented its new program yet.
But some other countries already have: starting in December 2017, Australian women are tested for HPV as the first stage of their cervical cancer screening. Ireland, after a mixup in its cervical cancer screening program in which many women weren’t told that they had a problematic result on their Pap smear, is also planning to add HPV testing to its program.
This doesn’t mean that the Pap test should be completely abandoned though. Follow-up screening, after a positive HPV test, could include a Pap test to look for abnormal cells.
Aside from the accuracy, there are other advantages of HPV testing. If someone got a negative result and didn’t have HPV, they probably wouldn’t need to be tested for another five years, rather than the current three, said Dr. Sheila Dunn, a physician and researcher with Women’s College Hospital.
“Women who don’t have it are very unlikely to have a problem,” she said. “Women who have it, they may not have a problem, but they need to be tested further to see if they do.”
Unfortunately though, moving to HPV testing wouldn’t mean an end to stirrups and a speculum in an examination room – at least not until at-home testing kits are improved. The test procedure is very similar to a Pap test and it’s unlikely the patient would notice much difference.