Using HPV Testing To Screen for Cervical Cancer
Cervical Cancer Screening
The current technique for screening for cervical cancer involves collecting cells by way of a pap smear and examining them under a microscope. Although this method has reduced cervical cancer in countries where it is regularly used, it has several weaknesses. A new study found that the test for human papillomavirus (HPV), which is present in almost all cervical cancers, is more sensitive than cytology (cell examination) in detecting cervical cancer. The study published online April 3, 2006 in the International Journal of Cancer, the official journal of the International Union Against Cancer (UICC), and is available via Wiley InterScience.
Cytology is currently the gold standard for cervical cancer detection, but it has several limitations: high-quality samples must be collected; identifying the cell changes that may lead to cancer is highly subjective; and the method itself is very repetitive, which can further lead to interpretive errors. Several studies have shown that HPV testing is more sensitive than cytology at detecting cervical intraepithelial neoplasia (CIN), the changes in cervical cells that can lead to cancer. The current study was an analysis of data from several countries comparing the two methods.
Led by Jack Cuzick, Ph.D., of the Cancer Research UK Department of Epidemiology, Mathematics and Statistics at Queen Mary School of Medicine in London, researchers performed an overview on patient data for more than 60,000 women in the United Kingdom, France, Germany, the Netherlands, the United States and Canada. They analyzed the comparison of HPV testing to cytology both overall and for different age groups. The results showed that HPV testing was very sensitive (96 percent overall) in all the studies and that this sensitivity was not affected by age of patient. Cytology was substantially less sensitive than HPV testing (53 percent overall, although results varied widely) but it was more effective in women over 50 than in younger women. HPV testing was less specific for women under 35, but for older women the differences in specificity between the two methods were quite small. Specificity refers to the percentage of people who are disease-free and who test negative. There will always be some people who do not have the disease, but who are positive for the screening test (HPV or cytology).
"While well-conducted screening programmes based on cytology have undoubtedly led to a large reduction of cervical cancer in some countries, the high variability in sensitivity reported here indicates the need for strict quality control," the authors note. "HPV testing is highly reproducible, more easily monitored, provides an objective test outcome and can easily be automated." Since only persistent HPV infections are thought to be associated with pre-cancerous lesions, they suggest that procedures need to be developed for repeat testing to detect infections that may be transient, especially in younger women. They also suggest performing the HPV test as the sole primary test, since it is the more sensitive of the two methods, and follow it with cytology, the more specific test, in those who test positive initially.
A recent statement from the International Agency for Research on Cancer (IARC) concluded that HPV testing could reduce the incidence and mortality from cervical cancer and that it is likely to be at least as effective as cytology. The English Cervical Screening Advisory Committee has recently accepted the IARC statement and agreed that the HPV test could be used by the national screening program. "These statements should be influential in establishing streamlined large-scale demonstration projects employing HPV testing as part of primary screening," the authors conclude. "Such projects are needed to determine how best to implement this new test, and to see if it can reduce invasive cancer rates below those now achieved with cytology-based programmes."