On June 8th, the FDA took a big step toward cervical cancer prevention by approving Gardasil™, a vaccine against human papillomavirus (HPV) . Infection with HPV, which is a common sexually transmitted virus in both men and women, may lead to cervical cancer in women. HPV is typically benign, causing genital warts or no symptoms at all, and is easily attacked by the immune system.

In some cases, though, the virus remains in a woman’s cervix, where it can cause precancerous changes. Gardasil™ targets four strains of HPV, two of which cause 70% of all cervical cancers. The vaccine is approved for girls and women ages 9-26, with the aim of preventing initial infection; Gardasil™ cannot treat an existing infection.

The HPV vaccine is best used in conjunction with regular screening, as Gardasil™ does not protect against all strains of HPV. In addition, women already infected with HPV will not benefit from the vaccine. But which screening method is best? To answer this question, a group of Italian researchers compared three methods of screening cervical cells for signs of cancer:

  1. Conventional Pap test–the sample of cervical cells is placed on a slide and examined for precancerous changes
  2. Liquid-based Pap test–the sample is suspended in liquid before being examined for precancerous changes
  3. HPV test–the sample is placed in a liquid and then tested for the presence of high-risk strains of HPV

This study, in the June 7, 2006 issue of the Journal of the National Cancer Institute , found that the HPV test was more sensitive than the conventional Pap test at detecting precancerous changes (ie, produced fewer false negative results), although the HPV test also resulted in more false positives than the conventional test.

About the Study

Researchers based in Turin, Italy recruited more than 33,000 women, ages 35-60, to take part in a study comparing three cervical cancer screening methods. Half of the women were given a conventional Pap test, while the other half was screened with two methods: the liquid-based Pap test and an HPV test.

To assess accuracy, the researchers calculated two factors: how often the test correctly identified precancerous cells in the cervix (sensitivity), and how often the test correctly identified the absence of precancerous cells (specificity). Tests with poor specificity tend to produce false positive results, which can lead to unnecessary additional testing and anxiety.

The HPV test—which was 41% more sensitive than the conventional Pap test—was most likely to correctly identify precancerous cells. The HPV test produced more false positives than the conventional Pap test, but less than the liquid-based test. When used alone, the sensitivity of the liquid-based Pap test was similar to the conventional version. When used with the HPV test, the liquid version boosted sensitivity a bit. However, the liquid-based test was also most prone to false positives.

The women in this study were 35 years and older. The usefulness of the HPV testing in younger women, among whom HPV infection is more common, has already been established in previous studies.

How Does This Affect You?

Now is the time to talk with your doctor about the best approach to preventing cervical cancer for you (and for your daughters). Women under 26 years old who have not been infected by HPV are good candidates for the HPV vaccine. Clinical trials of 21,000 women and teenage girls showed Gardasil™ to be safe and 100% effective in preventing the two most dangerous strains of HPV. Although these results are certainly promising, its true safety and effectiveness will only be known after its marketing to the public.

In addition, all women should be screened regularly with a pelvic exam and either a Pap test or HPV test. Along with this Italian study, previous research has pointed to the HPV test as an equal or better indicator of cervical cancer than the conventional Pap test, which remains the standard of care for cervical cancer screening in the US.

The main drawback of the HPV test is its greater rate of false positives. Researchers believe that a false positive HPV test is more likely in women under age 40, because HPV infection is common in this age group and usually resolves without leading to cancer. In women over age 40, HPV infection is less common and when it does occur, carries a greater risk of progressing to cancer. If you are over age 35 (the cutoff age in this study) or 40, ask your doctor if the HPV test is a better screening method for you. The American Cancer Society recommends that screening begin at age 18 or the onset of sexual activity, whichever comes first.