DNA Test Outperforms Pap Smear
By DONALD G. McNEIL Jr.
April 7, 2009
A new DNA test for the virus that causes cervical cancer does so much better than current methods that some gynecologists hope it will eventually replace the Pap smear in wealthy countries and cruder tests in poor ones.
Not only could the new test for human papillomavirus, or HPV, save lives; scientists say that women over 30 could drop annual Pap smears and instead have the DNA test just once every 3, 5 or even 10 years, depending on which expert is asked.
Their optimism is based on an eight-year study of 130,000 women in India financed by the Bill and Melinda Gates Foundation and published last week in The New England Journal of Medicine. It is the first to show that a single screening with the DNA test beats all other methods at preventing advanced cancer and death.
The study is “another nail in the coffin” for Pap smears, which will “soon be of mainly historical interest,” said Dr. Paul D. Blumenthal, a professor of gynecology at Stanford medical school who has tested screening techniques in Africa and Asia and was not involved in the study.
But whether the new test is adopted will depend on many factors, including hesitation by gynecologists to abandon Pap smears, which have been remarkably effective. Cervical cancer was a leading cause of death for American women in the 1950s; it now kills fewer than 4,000 a year.
In poor and middle-income countries, where the cancer kills more than 250,000 women a year, cost is a factor, but the test’s maker, Qiagen, with financing from the Gates Foundation, has developed a $5 version and the price could go lower with enough orders, the company said.
“The implications of the findings of this trial are immediate and global,” Dr. Mark Schiffman of the National Cancer Institute wrote in an editorial accompanying the study. “International experts in cervical cancer prevention should now adopt HPV testing.”
At the moment, there are huge gaps in how rich and poor countries screen.
In the West, women get smears named for their inventor, Dr. Georgios Papanikolaou. Cells are scraped from the cervix and sent to a laboratory, where they are stained and inspected under a microscope by a pathologist looking for abnormalities. Results may take several days.
The DNA screen also needs a cervical scraping, but it is mixed with re-agents and read by a machine.
In poor countries, most women get no routine screening. Pain sends them to a hospital, by which time it is often too late.
But in some countries, women get “visualization,” pioneered in the last decade, also with Gates Foundation support: a health worker looks at the cervix with a flashlight and swabs it with vinegar. Spots that turn white may be precancerous lesions, and are immediately frozen off. Diagnosis and treatment take only one visit.
Pap smears fail in the third world because there are too few trained pathologists and because women told to return often cannot.
The Indian study, begun in 1999, divided 131,746 healthy women ages 30 to 59 from 497 villages into four groups. One group, the control, got typical rural clinic care: advice to go to a hospital if they wanted screening. The second got Pap smears, the third got flashlight-vinegar visualization, and the fourth got a DNA test, then made by Digene, which is now owned by Qiagen. The company did not pay for or donate to the study, its authors said.
After eight years, the visualization group had about the same rates of advanced cancer and death as the control group. The Pap-smear group had about three-fourths the rates, and the DNA test had about half.
Significantly, none of the women who were negative on their DNA test died of cervical cancer. “So if you have a negative test, you’re good to go for several years,” Dr. Blumenthal said.
The study’s chief author, Dr. Rengaswamy Sankaranarayanan of the International Agency for Research on Cancer in Lyon, France, said, “With this test, you could start screening women at 30 and do it once every 10 years.”
Asked whether that advice would apply in the United States, Debbie Saslow, director of gynecologic cancer for the American Cancer Society, replied, “Absolutely no.”
“A negative test would mean a woman’s chances of developing cancer are small, but not zero,” she added. “But if he’d said five years, I wouldn’t have a strong reaction.”
Since 1987, she said, the cancer society and the American College of Obstetricians and Gynecologists have recommended Pap smears only every three years after initial negative ones. In 2002, they recommended the HPV test too, and evidence is mounting that the Pap smear can be dropped.
“But we haven’t been able to get doctors to go along,” Dr. Saslow said. “The average gynecologist, especially the older ones, says, ‘Women come in for their Pap smear, and that’s how we get them in here to get other care.’ We’re totally overscreening, but when you’ve been telling everyone for 40 years to get an annual Pap smear, it’s hard to change.”
Dr. Sankaranarayanan said most European countries screen every three to five years, and many do not start before age 30.
Cervical cancer is caused by a few of the 150 strains of the human papillomavirus. Women pick strains up as soon as they start having intercourse, but more than 90 percent of cases clear up spontaneously within two years. Early DNA tests would find these, but lead to useless overtreatment. So in women ages 20 to 30, doctors often order repeat Pap tests, which is expensive but may catch the tiny minority of cancers that develop in less than 15 years.
“The U.S. has high resources and low risk-tolerance,” Dr. Schiffman explained, while countries like India have little money and are forced to tolerate risk.
Dr. Jan Agosti, the Gates Foundation officer overseeing its third world screening, said Qiagen’s new $5 test — which proved itself in a two-year study in China — runs on batteries without water or refrigeration, and takes less than three hours. In countries where women are “shyer about pelvic exams,” she added, it even works “acceptably well” on vaginal swabs they can take themselves.
mardi, avril 07, 2009
dna test for cervical cancer
I'd love to take this test instead of getting into the stirrups.