Using a traditional Pap smear with a relatively new screening test for the virus that causes cervical cancer significantly improves the chances of early detection, according to new research published today.
The study of 12,527 women found that the combination of tests detected 51% more cancers and precancerous lesions in initial screenings than the Pap test alone.
The report in the New England Journal of Medicine provided fresh evidence of the benefits of the human papillomavirus screening test, which has been approved for use with Pap smears in the U.S. since 2003.
The HPV test detects genetic material from 13 types of HPV, a sexually transmitted virus that has been shown to cause cervical cancer. It differs from the Pap test, in which a sample of cervical cells is examined under a microscope for abnormalities.
The HPV test is more sensitive than the Pap smear, which sometimes fails to detect cancer. A shortcoming of the HPV test is that it also picks up the presence of transient viral infections that will never become cancerous.
American Cancer Society screening guidelines say the HPV test is a reasonable choice for women 30 or older who are also getting a Pap smear. The guidelines say the test combination should be administered every three years to reduce the chance of false-positive results triggered by transient infections.
Women who use only the Pap smear are screened every one to two years. The guidelines recommend against the HPV test for women younger than 30 because they are more likely to have transient infections.
The HPV test, marketed in the U.S. by Digene Corp., costs about $50, compared with $20 to $30 for a Pap smear.
The Pap test is widely regarded as the most effective screening tool for any cancer. Cervical cancer death rates have tumbled more than 75% since the mid-1950s and are expected to decline nearly 4% this year. The American Cancer Society estimates 11,150 cases of invasive cervical cancer will be diagnosed in the U.S. this year, and 3,670 women will die from the disease.
The study, conducted by Swedish researchers, divided women into two groups: One received both tests; the other had only a Pap smear. The women, ages 32 to 38, were tested at the start of the study and followed for an average of four years.
At the start of the study, 51% more cases of cervical cancer or precancerous conditions were detected in women who received both tests than those who received the Pap test alone. But by the end of the four-year period, the Pap test detected roughly the same number of cases.
The study did not last long enough to determine whether earlier cancer detection improved the life expectancy of the women who received both tests.
A second study, also published in the journal, reported that the HPV test was nearly twice as accurate as the Pap test at detecting precancerous changes in the cervix.
The study of 10,154 Canadian women ages 30 to 69 found that the HPV test detected 95% of abnormalities, whereas the Pap test detected 55% of possible cancer precursors.
The HPV test, however, had twice the rate of false positive results -- 6% compared with 3% for the Pap test.
The researchers, led by Dr. Eduardo Franco of McGill University in Montreal, recommended a shift to the HPV test from the Pap test.
But other experts said such a change would be premature, noting that the Pap test in the Canadian study was considered less accurate than the Pap test generally used in the U.S.
"The big problem with this study is that we don't know what its applicability is to us," said Dr. Carolyn D. Runowicz, an oncologist at the University of Connecticut's Carole and Ray Neag Comprehensive Cancer Center, who wrote an editorial accompanying the reports.