NEW YORK (Reuters Health) - The persistence of infection with a virus linked to cervical cancer may help determine which women develop the disease, study findings suggest.

Researchers say the findings could have implications for cervical cancer screening and for research into a vaccine against the viral strains behind the disease.

Their study showed that women infected with certain types of human papillomavirus (HPV) were more likely to show pre-cancerous changes in the cervix when their HPV infection persisted over several months.

There are more than 100 different types of HPV, including some that cause genital warts. A portion of these viruses are sexually transmitted, and some are linked to cancer. It is believed that certain ``high-risk'' HPVs are the primary cause of cervical cancer. However, HPV infection usually goes away on its own, and most women who get the virus do not develop cervical cancer.

``Most women clear the infection because of a good immune response,'' Dr. Eduardo L. Franco of McGill University in Montreal, Canada, noted in an interview with Reuters Health.

But for a minority of women, HPV infection persists. And Franco and his colleagues found that these women were more likely than others to show cervical abnormalities called squamous intraepithelial lesions (SIL), which sometimes become cancerous.

The HPV subtypes 16 and 18 were particularly predictive of these lesions, they report in the December 26th issue of the Journal of the American Medical Association.

The researchers conducted their study in Sao Paulo, Brazil. At the outset, women underwent Pap smears to get cervical samples, from which the investigators looked for HPV DNA to determine which, if any, virus subtype was present.

Of the more than 1,600 women followed, just 24 were positive for HPV 16 or 18 at two clinical visits, spaced 4 months apart. These women had the highest rates of ``high-grade'' SIL--lesions that are more likely than others to become cancerous. No woman who tested positive for HPV 16 or 18 at just one visit was found to have a high-grade lesion.

Another 38 women were positive for other cancer-linked HPVs on two consecutive visits. They were also more likely than other women to have a high-grade lesion or any SIL.

Overall, women with a persistent infection with a cancer-linked HPV were about 10 times more likely than women negative for HPV at both visits to show any type of SIL, according to the report. The actual rate of SILs for these higher-risk women was less than nine per 1,000 women per month.

Franco said these findings add to evidence that ``HPV persistence, rather than one-time detection,'' is key in the risk of cervical cancer.

In the US, HPV DNA testing may be done when a woman's Pap smear reveals abnormalities of ``indeterminate significance,'' Franco noted.

This study, his team concludes, supports the use of repeated HPV testing during screening to best assess risk.

And, Franco said, the findings bolster the argument to target HPV 16 and 18 in the current research into a vaccine. Thirteen HPVs are believed to be tumor-promoting, and narrowing down the subtypes to be included in a vaccine would boost its effectiveness, the researcher explained.

Exactly why only some women harbor persistent HPV is unknown. Franco said this a ``crucial question,'' and his team is currently looking into the genetic factors that may play a role.

Infection with a cancer-linked HPV produces no clear signs or symptoms, so women often don't know if they have ever been infected. However, regular Pap smears can catch cervical cancer early. Experts advise that all women who have been sexually active get routine pelvic exams and Pap smears.

SOURCE: Journal of the American Medical Association 2001;286:3106-3114.

Reference Source 108

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