Better Detector?

Test Targets Most Virulent HPV Strains

MCG researchers are studying a test for the two strains of human papillomavirus responsible for most cervical cancers.

The molecular assay uses a cervical scraping, like that for a liquidbased Pap smear, to test for HPV types 16 and 18, responsible for 70 percent of cervical cancers, said Dr. Daron G. Ferris, MCG family medicine physician and director of the Gynecologic Cancer Prevention Center.

“Data from a National Cancer Institute trial show 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,” said Dr. Ferris, a principal investigator on the national study evaluating the assay.

The NCI study followed women infected with different types of the typically slowacting virus over 10 years. It found women infected with type 18 had a 15 percent risk of cancerous or precancerous 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 12 percent.

 

The typespecific assay, developed by Third Wave Technologies, Inc., in Madison, Wis., is being tested along with an assay that detects 14 types of cancercausing HPV. A test that detects 13 types of HPV already is commercially available, so the new test could become the second nontypespecific 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 screening options for the most common sexually transmitted disease.

The current national study is giving the new HPV test and the typespecific 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 ASCUS—or highergrade abnormalities.

“These are the two ways to use HPV testing,” said 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 ASCUS Pap smear, which at best is about 80 percent accurate.

However, the HPV test, which is more accurate, has not become widely accepted as a primary screening tool for women age 30 and older, Dr. Ferris said, citing cost and the widespread use of Pap smears as likely factors.

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.

Younger women are another matter. Ages 15 to 25 are peak sexual activity years and peak years for HPV infection, said 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 said.

Lessexpensive Pap smears likely would continue to be used in the under30 group to catch the few infections that become problematic in this age group.

Currently, there are not FDAapproved drugs to cure cervical precancers and cancers caused by HPV, although centers such as MCG’s 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.

 

Toni Baker

 

The Medical College of Georgia is the state’s health sciences university with a tripartite mission of education, research and patient care.