Oct. 3, 2007 -- The Pap test has been used for more than six decades to detect cervical cancer and precancerous cells, but a different screening method may help in better identifying precancers early in women in their 30s and beyond, findings from a large European study suggest.
HPV testing could also lead to less frequent screening for women who are 30 and over, the researchers say.
HPV DNA testing is known to be more sensitive than the traditional Pap test, meaning that it is able to detect more cervical abnormalities early. But it has not been clear until now if these abnormalities were clinically relevant, says the study's principal investigator.
"We showed that these lesions were indeed clinically meaningful, and that HPV DNA testing leads to their earlier detection," Chris Meijer, MD, of Amsterdam's VU University Medical Center, tells WebMD.
He adds that HPV testing may eventually replace Pap testing as the first-line screening method for cervical cancer if longer follow-up confirms early findings.
HPV and Cervical Cancer
It is now clear that virtually all cervical cancers -- more than 99%, according to the American Cancer Society -- are related to HPV infection, which is a sexually transmitted virus. Just two strains of the virus, HPV 16 and HPV 18, account for 70% of cervical cancers. Most genital HPV infections don't cause cancer though.
Current screening guidelines in the U.S. call for annual Pap screening within three years of vaginal intercourse or no later than age 21. Beginning at age 30, low-risk women who have had three normal consecutive Pap smears can safely be screened less often.
In the U.S., HPV testing is approved in cases where Pap tests results are unclear or in conjunction with Pap screening after age 30. HPV testing is not a replacement for Pap testing.
In an effort to clarify the value of HPV testing in cervical cancer screening, researchers in the Netherlands have enrolled roughly 45,000 women in an ongoing comparison trial of HPV plus Pap testing vs. Pap testing alone.
Interim results involving just over 17,000 women between the ages of 29 and 56, enrolled in the study for an average of seven years, are reported in the Oct. 4 online edition of the journal The Lancet.
For the first five years of annual screening, about half the women got Pap tests and HPV tests to detect the presence of viral infection associated with cervical cancer and half got Pap testing alone. After five years, both tests were given to both groups.
In the follow-up analysis, women who had both tests early on also had earlier detection of lesions with the potential to lead to cervical cancer. However, the total number of these precancerous lesions was the same between the two groups over the two screening sessions.
Screening Less Often
The researchers conclude that HPV testing could lead to longer intervals between testing, raising the possibility that more women will be screened.
But HPV testing alone would not be a good strategy for screening women under 30 because so many young women have transient HPV infection, says Carmel Cohen, MD, Columbia University School of Medicine professor of obstetrics and gynecology.
"A younger woman who is positive for HPV is more likely to be negative again six months later," Cohen tells WebMD. "If we used the HPV test alone we would be putting younger women through a lot of needless follow-up testing."
Cohen says it remains to be seen if HPV testing will turn out to be a good single test for screening women who are 30 and older.
"Whether HPV positivity alone is an acceptable method of screening remains to be verified in studies with longer follow-up," he says.