Co-Testing for Cervical Cancer is Best, But Not Perfect

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Pap smear tests and HPV tests are designed in such a way that they help in early detection of precancerous and cancerous processes of cervical cancers so as to avoid contracting those cancers.

While co-testing catches more precancerous cells, it also raises the incidence of false positives, points out Dr. Diane Harper, a professor of medicine who researches HPV at the University of MI. For women under 25, the Task Force suggests use of Pap test alone because many of them are infected with HPV.

In a emailed statement to CBC News, Dr. Jennifer Blake, chief executive of the Society of Obstetricians and Gynaecologists of Canada, said: "Our HPV guideline is still in development, however we are supportive of HPV ... testing becoming integrated into provincial cervical cancer screening programs". "If women have a negative HPV test, they are significantly less likely to have a precancerous lesion four years later, meaning we can extend screening time". The goal was to examine the clinical utility of both tests to predict grade 2 or 3 cervical intraepithelial neoplasia (CIN) lesions (CIN2+ or CIN3+, respectively).

Leslie Massad, MD, a professor of obstetrics and gynecology at Washington University in St. Louis, wrote an editorial to accompany the study and agrees with its conclusion that HPV tests perform better than Pap tests. But one issue is that it was centered around one ideal system in British Columbia, where they had one place to send all of the Pap smears and HPV testing.

Because all the women in the study who testing negative for HPV were given Pap smears at the end of the study, the results can't determine how one test alone compares to co-testing. He called use of the HPV test only a "reasonable strategy" but noted that the test's strength - its sensitivity - could result in more positive results and more testing.

The cytology-based Pap smear involves looking for cancer or precancer cells by testing cells taken from a woman's cervix.

Schmeler often works in Latin America where, in countries like El Salvador, cervical cancer is one of the most common cancers in women primarily due to poor screening programs. "When we think about cervical cancer screening, we want to think about it in the framework of how do we get this test in the hands of all women?" "They usually take up to 10 years to progress to cancers, but the point is if you don't find them, and you don't know how long they've been there, there is a chance that they could progress to the invasive form of cervical cancer". "The real benefit of co-testing is with the HPV test", she said. However, it looks like neither test was completely certain, as abnormalities were found in women from both groups who tested negative previously.

Specifically, the task force is recommending either screening every three years with a Pap test alone or every five years with an HPV test alone for women aged 29 to 65.

Most cases are preventable with screening the best way of catching it before it develops. Infection with HPV types targeted by the vaccine has declined by almost two-thirds among teenage girls since HPV vaccination was recommended in the United States, according to a study that also found that there was a decrease in HPV infections among women 20 to 24. Two years later, the ones that tested negative after the Pap smear had another test of the same type. More than 4,000 women die from it, even with screening and treatment. If the guidelines change, and people over 30 switch to the HPV test, doctors will still most likely recommend that sexually active patients younger than 30 stick with the Pap smear. They can't rely on HPV testing, Schmeler says, because nearly everyone in that age group will contract HPV, and in many cases it goes away on its own.