When it comes to detecting cervical cancer, the Pap test has been the gold standard for more than 60 years. But as the role of human papillomavirus virus (HPV) in contributing to the cancer has emerged in recent years, screening for HPV has started to rival the Pap. And last week, a study of more than one million women added to HPV test's utility; it found that the HPV test was more successful in assessing cervical cancer risk than the Pap smear.
With a Pap smear, health care providers scrape cells from the surface of the cervix and analyze them under a microscope for abnormal ones that could turn in to cervical cancer. The HPV test, on the other hand, detects the presence of two strains of HPV, which is responsible for about 70% of cervical cancer cases.
In the recent study, published in the Journal of the National Cancer Institute, women with a negative HPV test had half the risk of developing cancer over three years as women who had a negative Pap test, and similar rates to women who were negative on both tests (known as a co-test). Because most cases of cervical cancer are caused by an infection with HPV, women who don't show signs of the virus are at a very low risk of developing the cancer --even lower than women who have a negative Pap test.
For that reason, says the study's lead author Julia Gage of the division of cancer epidemiology and genetics at the National Cancer Institute, "We think that HPV primary screening might be a viable alternative to Pap screening as well as co-testing."
The potential role of HPV testing as a first line screening tool for detecting cervical cancer is also supported by an April study published in the Lancet that looked at four randomized controlled trials in Europe and concluded that the HPV test was the superior screening method. Other studies in rural populations have also been able to cut down on advanced cervical cancers and deaths using just HPV screening.
That's why in April, the Food and Drug Administration unanimously approved an HPV DNA test developed by Roche as a primary screening tool for cervical cancer for women ages 25 and older. The test screens for the strains most commonly linked to the cancer -- HPV 16 and HPV 18 -- as well as for others. Along with the approval, the FDA offered guidelines for how the test should be used, advising that women who test positive for HPV 16 or HPV 18 should have a colposcopy, or a procedure that magnifies the cervix so physicians can take a better look at abnormal cells and take biopsies if needed. If women test positive for other strains of HPV, they should have a Pap test as a follow-up to determine the state of their cells.
Still, while the data appears to be showing that the HPV test is a more accurate predictor of cervical cancer, it's unlikely it will replace the Pap smear any time soon. "There’s not enough evidence accumulated to have a guideline revision at this point," says Gage. There's concern, for example, that HPV tests could lead to more unnecessary and invasive procedures, since just the presence of the virus doesn't always mean cancer will follow; many cases of infection resolve on their own.
And many physicians have relied on the Pap for so long, that implementation will not be prompt. "I understand that something that's gospel one year may not be gospel the next, but I still tend to lean towards doing the Pap smear than just an HPV test alone," says Dr. Mary Jane Minkin, a clinical professor of obstetrics, gynecology, and reproductive sciences at the Yale School of Medicine.
Most health groups have adopted a similar wait-and-see approach, relying on a combination of Pap and HPV tests. In 2012, for example, the U.S. Preventive Services Task Force (USPSTF) released updated guidelines for cervical cancer screening, advising Pap testing for women between the ages of 21 to 65 every three years, or co-testing with a Pap smear and HPV test every five years for women ages 30 to 65 with normal screening results. Younger women, experts believe, may be more likely to clear HPV infections so wouldn't benefit as much from regular HPV testing.
Now that studies are suggesting that HPV may be a useful addition, if not replacement, for Pap testing, doctors and their patients may be able to better exploit opportunities to detect and prevent cervical cancer and keep rates of the disease as low as possible.