A new Finnish study has confirmed that an HPV test picks up more pre-cancerous cells than a conventional pap smear, but experts don't agree on what this means for cervical cancer prevention programs.
Dr Ahti Anttila of the Finnish Cancer Registry in Helsinki, and colleagues, report their findings today in the British Medical Journal.
The large randomised trial studied over 58,000 women aged 30 to 60, who were invited to take part in a national cervical cancer screening program.
Cervical samples from some of the women were tested for HPV DNA, with follow-up cytology (examination of cervical cells) if the test was positive.
Others underwent the conventional cytological screening used in the 'pap smear'. The women were then tracked for a maximum of five years.
Anttila and colleagues found that there was a higher rate of detection of cells that can develop into cancer, in the women given the HPV test.
They say the findings are important for cancer prevention and urge the trialling of HPV as a primary screening tool.
Support for switching to HPV testing
Dr Brian Morris, Professor of Molecular Medical Sciences at the University of Sydney who has been involved in developing HPV tests in Australia says it is an "important study".
"This new research confirms years of research that had been suggesting that HPV testing should be used as the initial test for cervical screening and that only those who test positive for HPV should then undergo follow-up cytological testing," says Morris.
In Australia, HPV tests are currently used as a back-up test when problems are found, but not as a screening tool.
"The new findings add impetus to the need for the roll-out of HPV testing as the primary screening test in Australia and the rest of the world. The Australian Government should take note," says Morris.
But some researchers are a bit more cautious about what the study means for policy, especially in Australia.
Cytology differs between countries, as do screening programs. For example in Australia women over 18 are screened every two years, whereas in Finland only women over 30 are screened every 5 years.
"It's quite a different context to ours," says Dr Deborah Bateson, Senior Medical Co-ordinator for Family Planning New South Wales.
Cytologist Annabelle Farnsworth of Douglas Hanly Moir Pathology says Australia has one of the highest standards of cytology and would have to do its own study to determine the comparative sensitivity of HPV tests.
Morris says HPV testing has an advantage in that it can be done on samples collected by a woman herself, such as by use of a tampon.
This means that more women could participate in screening says Morris, who has been involved in the development of a self-sampling kit.
"Women who are too busy or who don't participate in screening because they don't like it (are embarrassed, find it uncomfortable, or have cultural or religious objections) can easily get screened by collecting their own sample and then sending it (via a pharmacy or by mail) to a lab for testing," says Morris.
Farnsworth is concerned about the reliability of samples taken by people in their own home.
But her and Bateson have other concerns about the widespread use of HPV tests as a screening tool.
Risk of over-testing
HPV is transmitted sexually and is most often detected in young women. Some types of the virus cause genital warts whereas others cause cancer, including cervical cancer.
HPV tests detect viral DNA whereas cytology picks up changes in the cells, which occur in the presence of the virus.
Farnsworth and Bateson say HPV tests may be more 'sensitive' than cytology but they are less 'specific', and they are concerned about the potential of over-testing.
"Just having a positive HPV test by itself isn't always associated with disease," says Bateson likening HPV to a cold virus.
"We know that some people will clear the virus and they won't have any long-lasting effect on their risk of developing cervical cancer."
Bateson say HPV infection is only a problem when it persists and cytology is required to confirm cells have become abnormal.
Farnsworth likens the debate over HPV to that over PSA tests for prostate cancer.
"Yes it picks up abnormalities, but it also picks up a whole lot of stuff you don't want to know about," she says.
Farnsworth says cytology may be less sensitive but its specificity makes it a good screening test.
"If you repeat it over 2 or 3 years, you get almost everything," she says.
Careful application of HPV test
Because HPV is so common in younger women, Bateson does not think using an HPV test as a screening tool in this age group would be a good idea.
"If you did an HPV test on all young women and then you did a pap smear on all young women who were positive you'd be doing a lot of double testing which may not have any impact on the disease outcome," says Bateson.
She says HPV screening may be more appropriate in older women.
"There's a lot of debate on this and a lot of people looking at the optimal ways of going about the screening program," says Bateson.
"With any screening test it's always a matter of balance between picking up enough, and not picking up things that wouldn't really need an intervention anyway, leading on to over-investigation."