HPV test should replace Pap test for cervical cancer screening, study suggests

The Pap test that has been used for decades as the standard in cervical cancer screening for Canadian women should be replaced by a test that detects high-risk types of human papillomavirus (HPV), a new study says. 

The virus is associated with the vast majority of cervical cancers. 

Whether they receive a Pap test or HPV test, the experience for patients is the same in their doctors' or nurse practitioners' offices. Women have the same physical exam whereby their cervix is swabbed for cells. The difference happens when that sample is sent to the lab for analysis.   

The clinical trial, conducted in B.C. and published in the Journal of the American Medical Association (JAMA), randomly divided about 19,000 women into two groups. The control group had the traditional Pap test for their initial screening, while the test group had primary HPV screening — a test that looked for more than a dozen specific types of HPV most likely to cause precancerous lesions in the cervix.  

The HPV test found almost 60 per cent more precancers — or abnormal cells that could potentially become cancerous —  during the initial screening than the Pap test, said study co-author Dr. Dirk van Niekerk, a pathologist who is also the medical leader of the cervical cancer screening program at the B.C. Cancer Agency.  

That kind of early detection is the hallmark of cervical cancer prevention, because health-care providers can take action to treat precancerous cells before they become cancer. Depending on the "grade," or how far advanced they are, they may simply require monitoring (because in younger patients, the cells sometimes repair themselves on their own)

Alternatively, they can be removed with laser treatment or with an electrical wire loop — a procedure known as "LEEP."

"The pre-cancerous stage is essentially 100 per cent curable," van Niekerk said. "They usually take up to 10 years to progress to cancers, but the point is if you don't find them, and you don't know how long they've been there, there is a chance that they could progress to the invasive form of cervical cancer."

'Better detection earlier'

The Pap test identifies abnormalities in cervical cells, flagging health-care providers to take a closer look to see if they are precancerous, and then take appropriate action. 

The HPV test is DNA-based, and looks for specific strains of the virus in the sample.  

In addition to finding more precancers in the initial screening, women who had the HPV test had a "significantly lower likelihood" of having precancer in the cervix when they exited the study four years later.

That's likely because women who tested positive for precancer or abnormal cells at the beginning received additional testing and treatment as necessary, van Niekerk said.

There have been other clinical trials that have found HPV testing to be an effective screening tool in conjunction with the Pap test, van Niekerk said, but this was the first trial to compare the two in isolation from each other.  

Dr. Nancy Durand, a gynecologist at Sunnybrook Health Sciences Centre in Toronto who was not involved in the study, said it is a "huge step at providing very specific evidence" that the HPV test should replace Pap tests as the standard of care — something she believes will happen in the coming years.

The trial showed the HPV test provides "better detection earlier" of the people at risk "that we really need to be following more closely," Durand said. 

"Not all of them will require treatment.  Some of them won't.  But we don't want to miss people who have potentially high-grade precancerous disease and they don't know it and they could go on to be at higher risk for developing invasive cervical cancer."

Although there could be increased costs associated with sending more patients for additional tests and monitoring after HPV detection, those may be offset by the fact that people may not need to have the initial screening as often, she said.   

In most provinces, Pap tests are recommended every three years. The HPV test may only be needed every five years, Durand said, "because it's such an accurate test."

Because health care is a provincial responsibility, it's up to the individual provinces and territories to decide whether to adopt HPV testing instead of Pap testing for cervical cancer screening. 

Some countries have moved to using HPV in primary screening already, Durand said.   

In a emailed statement to CBC News, Dr. Jennifer Blake, CEO of the Society of Obstetricians and Gynaecologists of Canada, said: "Our HPV guideline is still in development, however we are supportive of HPV molecular testing becoming integrated into provincial cervical cancer screening programs."