The Pap smear, which has led to a 70% drop in the U.S. cervical cancer death rate over the past six decades, is moving closer toward obsolescence as a primary screening test for the disease in women 30 and older, conclude the authors of a Canadian study out today.

The researchers enrolled more than 10,000 women ages 30-69 in their study comparing the Pap smear, named for developer George Papanicolaou, with a test for human papillomavirus, or HPV, certain types of which cause virtually all cervical cancer cases. All of the women were screened with both tests, but they were randomly assigned to get either a Pap smear or an HPV test first.

As smaller, less-rigorous studies have found, the HPV test picked up far more cervical pre-cancers than the Pap smear did, the researchers write in The New England Journal of Medicine. "The paper clearly comes across strongly in favor of HPV testing as a primary screening test," says senior author Eduardo Franco, a cancer researcher at Montreal's McGill University. Only women who test positive for a cancer-causing HPV type would then have a Pap smear, Franco says.

One concern about the HPV test has been a higher rate of false positives due to its superior sensitivity, but Franco's study found only a small difference between the two screening tools. He calls the increased rate a false positives, which could lead to unnecessary additional testing, a fair tradeoff for detecting far more cervical pre-cancers — 94% vs. 55% — and, probably, allowing women to screen less frequently. The most recent American Cancer Society guidelines, issued in 2002, recommend that women with negative HPV tests and Pap smears wait three years before being screened again.

Only one Food and Drug Administration-approved HPV test, made by Digene of Gaithersburg, Md., a Qiagen company, is sold in the USA. It is approved only for use in women over 29 as a follow-up to inconclusive Pap smear results or as a "co-test" done at the same time as a Pap smear. It is not approved as a stand-alone primary screening test. About one out of four women who are eligible for the Digene HPV test currently are getting tested, Qiagen spokesman Jeff Schmalz says.