A single clinical HPV DNA test can predict a woman’s cervical cancer risk for at least the next 18 years, identifying women who already have invasive cervical cancer and those whose HPV infections will develop into disease in the future, according to a report published online July 30 in the Journal of Clinical Oncology.
In contrast, Pap smears cannot predict clinically important disease beyond 1-2 years, said Dr. Philip E. Castle of the American Society for Clinical Pathology, Washington, and his associates.
"An HPV test provides greater reassurance against cervical intraepithelial neoplasia grade 3 and cervical cancer than Pap testing and thus might be used as the screen to rule out disease in healthy women, whereas Pap is useful as a secondary diagnostic test to identify HPV-positive women at immediate risk of" invasive cervical cancer, they noted.
Dr. Castle and his colleagues analyzed data from a Portland, Ore., cohort of 19,512 women who underwent routine cytologic screening when they were aged 16-94 years at baseline in 1989-1990. Cervicovaginal lavages were retrospectively tested for HPV DNA through a commercially available diagnostic test used routinely in clinical practice.
The study subjects were followed for approximately 18 years with annual Pap smears. A total of 199 cases of invasive cervical cancer (cervical intraepithelial neoplasia grade 3+) were diagnosed during this time; 396 cases of CIN2+ were detected.
A positive Pap smear at baseline strongly predicted cervical cancer within 2 years, but not beyond that point. In contrast, a positive HPV DNA test continued to predict cervical cancer until the end of the study.
For example, HPV-positive women were more likely to be diagnosed as having CIN2+ and CIN3+ 10-18 years after enrollment, compared with HPV-negative women, while women with a positive Pap smear result were not more likely to be diagnosed with CIN2+ or CIN3+ than women with a negative Pap test, Dr. Castle and his associates said (J. Clin. Oncol. 2012 July 30 [doi:10.1200/JCO.2011.38.8389]).
Similarly, a one-time negative HPV test at enrollment "provided greater reassurance over the 18-year follow-up" than a one-time negative Pap smear against CIN2+ (1.85% vs. 2.47%) and CIN3+ (0.90% vs. 1.27%), they said.
More cases of CIN2+ (215 vs. 136 cases) and CIN3+ (112 vs. 65 cases) developed after an HPV-positive result than after a positive Pap result. And among women who were positive for HPV DNA at baseline and who went on to develop CIN2+ or CIN3+, only half had positive Pap smear results.
These findings "provide additional support for the use of HPV testing in routine screening" in women 30 and older, Dr. Castle and his associates said.
Moreover, the results of other studies have suggested that HPV testing also may help identify women at risk for cervical adenocarcinoma in situ and invasive adenocarcinoma – two disorders that "are poorly detected by cytology-based screening alone," the investigators said.
This study was supported in part by the National Cancer Institute. Dr. Castle reported ties to Merck, Qiagen, and Roche, and his associate, Dr. Attila T. Lorincz, reported ties to Qiagen.