Study: New Test Twice As Good As Pap Smear

A relatively new screening test was about twice as accurate as the traditional Pap smear at spotting cervical cancer, according to the first rigorous study of the test in North America.

The new test could replace the 50-year-old Pap in a matter of years, experts say. And there is a bonus for women: They will not need a screening test as often.

CBS News medical correspondent Dr. Jon LaPook reports how the new test works: "The HPV test is looking for the virus that actually causes the cancer of the cervix and that turns out to be better, more sensitive than when you actually look at the cells under the microscope in a Pap smear and look for the abnormal cells themselves."

The HPV test correctly spotted 95 percent of the cancers, while the Pap test only found 55 percent, according to researchers at McGill University in Montreal, who published their findings in Thursday's New England Journal of Medicine.

"We've had the Pap test for over 50 years and it's high time it be replaced by technology that's more robust," said Eduardo Franco, director of McGill's division of cancer epidemiology, who led the study.

Franco said some feared the HPV test would result in more false alarms, causing anxiety and requiring more follow-up testing. In the study, there were only slightly more false positives for the HPV tests (6 percent) than the Pap smears (3 percent).

But Dr. LaPook told Evening News anchor Katie Couric that the higher number of false positives plus the higher cost of the new test means that the Pap smear would still be an important diagnostic tool.

"The Pap smear, it's been the greatest screening test for cancer that we've ever had. So we're not ready to throw it out yet," he said.

HPV, or human papilloma virus, is a common sexually transmitted disease. Infections are mostly in young women and most go away on their own. The HPV test looks for the high-risk viruses that can cause cervical cancer if the infection persists. Like the Pap, it uses cells scraped from the cervix, the lower part of the uterus.

Because the Pap test misses about half of the cases, doctors use frequent testing to catch the slow developing cancer at its earliest, most treatable stages.

The HPV test has been available in the U.S. since 2000 and was first used for inconclusive Pap tests. Now women over 30 can get a HPV test - but only along with a Pap - and wait three years to be tested again if both tests are negative.

More recently, scientists have been studying whether the HPV test can be used alone and whether it can prolong the intervals between exams. Debbie Saslow, director of breast and gynecologic cancer for the American Cancer Society, said evidence from a number of studies supports using the HPV test in place of a Pap.

"Overall, I don't think there's any doubt that HPV testing has a lot of advantages over the Pap test," she said.

Saslow said there are still issues to be resolved, and federal approval needed, but "it's definitely coming." She said experts expect that to happen sometime in the next decade.

A Swedish study also in the journal compared Pap with HPV testing to Pap alone in 12,527 women in their 30s. They found the combo test detected precancerous lesions or cancer earlier than the Pap test alone.

The Canadian study, which was government-funded, included 10,154 women ages 30 to 69 in Montreal and St. John's, Newfoundland. The women got both tests. Still to be determined is the best way to start using the HPV test by itself and what follow-up action to take after positive results, the researchers said.

The HPV test is more expensive: In the U.S., the government health insurance program Medicare pays about $50 for the HPV test and $15 to $28 for a Pap test.

Some of the researchers have received fees or grants from drug makers including Merck Frosst Canada Ltd., a subsidiary of Merck & Co., which makes a cervical cancer vaccine. One has stock in Digene Corp., which developed the only approved HPV test.

Franco emphasized that girls who have been vaccinated against HPV will still need to be screened because the vaccine only protects against some of the cancer-causing strains.

Dr. Carolyn D. Runowicz, who wrote a journal editorial, noted that the two studies used a different kind of Pap test, not the liquid-based technology used in the U.S, which may be more sensitive. The results of a British study that used liquid Pap are due to be presented in November.

"We're not ready for prime time. We're moving in that direction. But we're not there yet," said Runowicz, a former president of the American Cancer Society.