New test for most virulent HPV strains under study
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