HPV tests better at finding cervical cancer than Pap tests: study
A DNA-based screening test for cervical cancer is substantially more effective at picking up evidence of cancer and pre-cancerous lesions than the cancer screening world's stalwart, the Pap test, two new studies suggest.
The two research groups, publishing Thursday in the New England Journal of Medicine, showed that a newer test that looked for DNA of human papillomaviruses (HPV)— which cause cervical cancer— found between 40 and 50 per cent more cancerous and pre-cancerous lesions than a single Pap test.
One of the groups, from Montreal's McGill University, suggested that a shift to the DNA test, coupled with increased use of the new HPV vaccination and education "will contribute to a more efficient control of cervical cancer."
"What we found, with very strong results, is that HPV testing is more sensitive than Pap testing— almost twice as much," lead author Dr. Marie-Helene Mayrand said in an interview from Montreal.
But she and others cautioned that a wholesale switch of testing regimes won't happen overnight.
"Are we ready now to abandon and throw away the Pap smear? My conclusion was we're not there yet," said Dr. Carolyn Runowicz, a gynecological oncologist at the University of Connecticut Health Center and a former president of the American Cancer Society.
"I think if you are looking on the horizon, and you're looking ahead 10 or 15 years, that these molecular tests may be a part of how we screen for cervical cancer," said Runowicz, who wrote an editorial that accompanied the studies in the journal.
The McGill-led study randomly assigned 10,154 women aged 30 to 69 in Montreal and in St. John's, N.L., to be screened using either the HPV DNA test or the traditional Pap smear.
HPV DNA test caught more cancers
Three per cent of women in the Pap test arm were found to have a cancerous or pre-cancerous lesion; that rate was six per cent in the HPV DNA group. The DNA test was found to have caught 94 per cent of the cancers or pre-cancers in the group compared to 55.4 per cent by the Pap test.
The second study of 12,527 Swedish women aged 32 to 38 showed that a testing regimen combining DNA testing with Pap smears found 51 per cent more cancerous and pre-cancerous lesions than the Pap test alone.
But because the DNA test is so much more sensitive, it can also pick up current HPV infections that women might go on to recover from— providing so-called false positive tests. And in the McGill study it was found that the DNA test was 2.7 per cent more likely than the Pap test to produce a false positive.
False positives are a concern in cancer screening because even though doctors know not all positive tests will lead to cancer if left untreated, they generally cannot tell which will and which won't. That means they end up treating people who don't need surgery, chemotherapy or whatever the treatment regime is.
"From a woman's point of view, that would result in incredible anxiety and testing," Runowicz said.
Under 30s could have many false positives
As well, the fact that the DNA test would produce a positive result in the face of an active HPV infection means the test probably wouldn't be of much use in women under 30, a group in which the prevalence of HPV infections is high.
Mayrand cautioned that women should not assume from these studies that Pap tests don't work. Even though it isn't the most sensitive of tests, the fact that women have one every year or two leads to a diagnosis of this slow developing cancer in most cases, she said.
"I wouldn't want any women looking at results of the study and concluding the Pap test is not good, I'll stop having Pap smears. That would be the worst-case scenario," she said.
While DNA-based cervical cancer testing may lead to earlier discovery— and easier treatment— of cervical cancers, it won't change the testing experience for women. The test is not blood based; it requires inserting a tiny brush into the cervical canal.
While cervical cancer remains a major cancer killer in the developing world, in Canada it is estimated that only 1,350 cases of the disease will be diagnosed this year and 390 women will die from it.