Coupling screening for a common sexually transmitted virus with the Pap test could help doctors identify which women are most prone to cervical cancer.
Women who have abnormal cervical cells and who test positive for the human papilloma virus are at much higher risk of having early forms of cancer, new research shows.
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As many as 2.5 million American women a year have abnormal Pap tests, turning up potentially cancerous tissue called atypical squamous cells of undetermined significance, or ASCUS.
While the vast bulk of these won't go on to become cervical cancer, the presence of ASCUS prompts follow-up, in the form of additional Pap smears and cell biopsies, that's both costly and worrying.
"If you can somehow pick out those patients who have the borderline Pap smears that need those [follow-up] tests, that would be of some utility, definitely," says Dr Fidel Valea, director of gynaecologic oncology at the State University of New York.
Cervical cancer will strike nearly 13 000 women in the United States this year and kill 4 400. But that's only a small fraction of the number of deaths that occurred before the advent of early detection methods for the disease.
In the latest study, the researchers followed 3 488 women with ASCUS, who received one of three options: some had immediate colposcopy, a close-up look at cervical cells often resulting in biopsy; some had an HPV test first, then colposcopy based on presence of the virus; and a third group had colposcopy only after additional Pap smears.
Screening for HPV, identified 96.3 percent of the women whose ASCUS ultimately became pre-cancerous. For repeat Pap tests, that figure was 85 percent.
Biopsies unnecessary for many HPV screening also helped determine which women weren't likely to have cervical tumours. Those who tested negative for the virus had a 99.5 percent chance of having healthy cervical cells. This group, which made up 45 percent of the subjects, was spared a biopsy.
Although the HPV test appears to be highly accurate, it's not for everybody, the researchers say.
"We don't feel that every woman in the US should get an HPV test, because [the virus] is very common," says Dr Mark Schiffman, an NCI cancer epidemiologist and co-author of the study. Among some groups, like sexually active college students, rates of HPV infection can be as high as 80 percent, he says.
The question now, Schiffman says, is how to use the various screening techniques in a cost-effective fashion. The HPV test runs roughly $50 a pop, equal to three or four Pap smears. Colposcopy can cost anywhere from $10 to $15, to as much as several hundred dollars when performed by expensive specialists.
"Before anyone can say that one technique is better than another we need formal cost-utility analyses," says Schiffman, whose group is now doing such reviews.
Vaccine safe so far In a separate study also appearing in the journal, researchers report success in a preliminary safety study of a vaccine against HPV. Patients who received injections of the vaccine, based on fragments of a strain of the virus, had a powerful immune response to the shot without any serious side effects.
The vaccine is so far only designed to guard against infection with HPV 16, the form of the virus linked to about half of cervical cancers. Scientists hope to cover as much as 80 percent of the virus-related cancers by combining a number of vaccines against HPV strains into a single shot.
If the current version does prevent HPV infection, "then the proof of principle will be there, and we'll have tremendous hopes of a combination vaccine," Schiffman says.
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