A test for the two strains of human papillomavirus responsible for most cervical cancers is under study.
The molecular assay uses a cervical scraping, like that for a liquid-based Pap smear, to test for HPV types 16 and 18, responsible for 70 percent of cervical cancers, says Dr. Daron G. Ferris, family medicine physician and director of the Gynecologic Cancer Prevention Center at the Medical College of Georgia.
“Data from a National Cancer Institute trial shows that if you have a genital infection with HPV types 16 or 18, your chance of getting moderate to severe precancerous cervical changes or cancer is much higher than if you have one of the other types,” says Dr. Ferris, a principal investigator on the national study evaluating the assay.
The NCI study followed women infected with different types of the typically slow-acting virus over 10 years. It found women infected with type 18 had a 15 percent risk of cancerous or pre-cancerous changes after 10 years, those with type 16 had a 20 percent increased risk while those with the 11 other strains had a collective risk of 1-2 percent.
“Clearly, there is a big difference between HPV types 16 and 18 and all the other cancer-causing strains of HPV,” says Dr. Ferris.
The type-specific assay, developed by Third Wave Technologies, Inc., in Madison, Wis., is being tested along with an assay that looks for the presence of 14 types of cancer-causing HPV. A test that detects 13 types of HPV already is commercially available, so the new test could become the second non-type-specific HPV test on the market.
Dr. Ferris, who was involved in early studies of the HPV vaccines, hopes the new tests will one day provide better options for screening for the most common sexually transmitted disease.
The current national study is giving the new HPV test and the type-specific assay to 1,500 women age 30 and older with a negative Pap test and to 1,000 women age 18 and older with cervical cell changes of undetermined significance – pathologists call this most common abnormal result ASC-US – or higher-grade abnormalities.
“These are the two ways to use HPV testing,” says Dr. Ferris. “One is as a primary screening adjunct test with a Pap test for women age 30 and older and the other is as a triage test when women have an abnormal Pap smear result.”
An HPV test typically follows an ASC-US Pap smear which at best, is about 80 percent accurate, he says.
However, the HPV test, which is more accurate, has not become widely accepted as a primary screening tool for women age 30 and older, he says, citing cost and the tradition of Pap smears as likely factors.
“This new HPV test could lengthen the interval of screening for cervical cancer. If the new test is as good as the old one and if the HPV test is negative, there is only a 1 percent chance you actually have something wrong,” he says, noting that Pap smears really don’t add much to the equation.
Still, when he lectures around the country and asks for a show of hands of physicians using HPV tests in women over 30, few go up; he hopes that will change.
“I think it’s a possibility in the future that we won’t be doing Pap smears on women over 30; it might just be screening with an HPV test. A lot of experts are suggesting maybe that is the way we should go,” he says.
In fact, the American College of Obstetricians and Gynecologists and American Society for Colposcopy and Cervical Pathology already recommend HPV testing in all women over 30.
Women under 30 are another matter. Ages 15 to 25 are peak sexual activity years and peak years for HPV infection, says Dr. Ferris. Fortunately, the vast majority of the infections are cleared; ones that persist to age 40 are most likely to cause problems. “Seventy percent of patients clear the infection. The 30 percent who don’t, if they still have it by the time they are age 40, are heading down the wrong path,” he says. Less expensive Pap smears likely would continue to be used in the under-30 group to catch the few infections that become problematic in this age group.
Currently, there are not FDA-approved drugs to cure cervical pre-cancers and cancers caused by HPV, although centers such as MCG are evaluating potential therapies. Resulting cervical changes may be followed with frequent Pap smears or colposcopy, in which physicians can view the cervix and freeze, excise or vaporize significant cellular changes.
For more information about the study, call Study Coordinator Ansley Dennis in Dr. Ferris’ office at 706-721-2535.
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