CHICAGO — A test for the human papilloma virus that doesn't require a pelvic exam may soon rival the Pap smear as an accurate way of screening for cancer and precancerous conditions, researchers reported Wednesday in the Journal of the American Association.
However, the two studies found that the new test produced far more false-positives than the Pap smear, causing many more women to need further testing.
Whether the human papilloma virus, or HPV, test's widespread use will ever be feasible, affordable and effective at reducing cervical cancer deaths remains to be seen, said an expert who was not involved in the work.
As a screening technique, the test may be most applicable in developing countries, where pelvic exams and lab exams of cervical cells are often unavailable, said the expert, Dr. Jack Cuzick of the Imperial Cancer Research Fund in London.
But the lead author of one of the studies said the test's false-positive rate may be much lower among U.S. women — and similar to that of the Pap smear — because they have much lower rates of sexually transmitted diseases than African and Central American women studied.
"I think for women over age 35 to 40, HPV testing will end up, in the near future, replacing a regular Pap smear," said the author, Dr. Thomas Wright Jr. of Columbia University.
The HPV test is now licensed in the United States only as a follow-up to an abnormal Pap smear. It has not been approved for routine screening, though it is available for that purpose in other countries.
The test is based on the discovery that the sexually transmitted HPV causes almost all cases of cervical cancer.
HPV infects an estimated 40 million Americans and many more worldwide. Though most of HPV's 80 strains cause no permanent harm, perhaps 1 percent of infected people get a strain that can cause cervical cancer.
Worldwide, almost 360,000 cases of cervical cancer were detected in 1990, with 190,000 women dying of the disease.
The Pap smear, which costs $25 to $35, is the most widely used screening test. It requires a skilled professional to do a pelvic exam and scrape cells from a woman's cervix. The cells are then analyzed under a microscope.
"A single Pap smear misses about 40 percent of cervical disease, which is why women are told to have yearly Pap smears," Wright said.
In HPV testing, which costs $45 to $60, women themselves can collect a sample of cervical tissue at a clinic or doctor's office using a small brush or cotton swab. The tissue is then analyzed for DNA from 13 types of HPV considered to be the main culprits in cervical cancer.
Wright's team and colleagues from AVSC International and the University of Cape Town screened and followed 1,365 black South African women ages 35 to 65. The researchers found that the HPV test identified 37 of 56 women with high-grade cervical disease or cancer, for a detection rate of 66 percent.
The Pap smear identified 38 of the 56 women, a rate of 68 percent. But the false-positive rate for the self-collected HPV test was 17 percent, vs. only 12 percent for the Pap smear.
In the other study, led by Dr. Mark Schiffman of the National Cancer Institute, researchers screened 8,554 women in Costa Rica ages 18 years and older. A total of 138 cases of high-grade cervical disease or cancer were found, with the HPV test detecting 88 percent and the Pap smear 78 percent. But HPV had almost twice the rate of false-positives, 11 percent, vs. 5.8 percent for Pap smears.