According to the results of a study published in the New England Journal of Medicine, testing for high-risk types of human papillomavirus (HPV) detects a higher proportion of precancerous changes to the cervix than conventional Pap testing, but also produces more false-positive results. A second study published in the same issue assessed the combination of HPV testing and Pap testing.
Human papillomaviruses (HPV) consist of more than 100 different viruses. Some types of HPV cause warts on the hands or feet; others cause genital warts; and some have been linked with cancer, most notably cervical cancer. The types of HPV most commonly linked with cervical cancer are HPV 16 and HPV 18, but several other high-risk types contribute to cancer as well.
The types of HPV that cause cervical cancer or genital warts are transmitted sexually. HPV infection is extremely common and generally occurs soon after an individual becomes sexually active. Although most infections resolve on their own, some persist and can lead to precancerous or cancerous changes to the cervix, vulva, vagina, penis, and anus.
Use of vaccines-such as Gardasil®-to prevent infection with high-risk types of HPV should reduce the occurrence of cervical cancer in the future. Because the vaccines do not prevent infection with all high-risk types of HPV, however, screening for cervical cancer will remain important.
The traditional screening test for cervical cancer is the Pap test, in which cells are removed from the cervix and evaluated for abnormal changes. More recently, researchers have explored the role of HPV testing in cervical cancer screening. Currently, HPV testing may be used in combination with a Pap test, or for further evaluation of women with an indeterminate Pap test. There is limited information, however, about whether the HPV test can be used alone as the initial cervical cancer screening test.
To compare HPV testing to conventional Pap testing for cervical cancer screening, researchers in Canada conducted a study among more than 10,000 women between the ages of 30 and 69 years. All women received both an HPV test and a Pap test. Women who tested positive on either test were referred for further evaluation by colposcopy.
- HPV testing detected 94.6% of cases of high-grade precancerous changes to the cervix (cervical intraepithelial neoplasia grade 2 or 3), compared to 55.4% for the Pap test.
- Among women without cervical abnormalities, 5.9% received a false-positive test result by HPV testing, compared to 3.2% by Pap testing.
These results indicate that among women between the ages of 30 and 69 years, HPV testing detects a higher proportion of high-grade precancerous changes to the cervix than Pap testing, but also produces more false-positive test results. Additional testing (such as follow-up Pap testing) or other triaging of women with a positive HPV test may reduce the number of women who need to be referred for colposcopy.
A second study, published in the same issue of the New England Journal of Medicine, compared the combination of HPV testing and Pap testing to Pap testing alone. The study enrolled more than 12,000 women between the ages of 32 and 38 years.
- Compared with women who received Pap testing alone, women who received both Pap testing and HPV testing were 51% more likely to have precancerous or cancerous changes identified at the initial screen and 42% less likely to have them identified at subsequent screens.
The researchers conclude: “The addition of an HPV test to the Pap test to screen women in their mid-30s for cervical cancer reduces the incidence of grade 2 or 3 cervical intraepithelial neoplasia or cancer detected by subsequent screening examinations.”
Although questions still remain about the optimal way to use HPV testing for cervical cancer screening, these studies suggest that HPV testing detects more cervical abnormalities than Pap testing alone. It should be noted, however, that both of these studies involved women over the age of 30. HPV testing may be less useful in younger women because HPV infections are very common in young women, and often resolve without causing problems.