By Nathan Seppa, Science News
A test for human papillomavirus infection is better than the standard Pap smear at catching cervical cancer early, researchers report. The study of women age 30 and over makes the case for changing cervical cancer screening practices, particularly in low-income countries, since the screening test for HPV would necessitate fewer doctor visits, scientists report in the April 2 New England Journal of Medicine.
“The implications of the findings of this trial are immediate and global,” declare Mark Schiffman and Sholom Wacholder of the National Cancer Institute in Bethesda, Md., in the same issue of NEJM. HPV testing should now be widely implemented in poor countries, they say.
Researchers randomly assigned more than 130,000 women age 30 to 59 in rural India to one of four equal-sized groups. Three groups underwent screening for signs of cervical cancer. Of those, some received a test for HPV types known to cause the cancer, others got a Pap smear and the third group received a visual cervical examination. Women in a control group were advised to seek medical care on their own. If any test showed a woman had an HPV infection or abnormal cell growth on her cervix, she was given a full exam and treated further as necessary. Thorough removal of precancerous lesions prevents cervical cancer.
The scientists started performing these initial screen-and-treat sessions in 2000 and assessed the women’s health in 2008 using a medical registry, hospital data and house-to-house surveys, says study coauthor Rengaswamy Sankaranarayanan, a radiation oncologist at the World Health Organization’s International Agency for Research on Cancer in Lyon, France.
The three screening tests turned up similar numbers of cervical cancer at the outset of the study. But women getting the HPV screen were less likely to develop any advanced-stage cervical cancer over the course of the study. And by the end of the study, 34 women who got the HPV screening had died of cervical cancer, compared with 54 in the Pap smear group, 56 in the visual exam group and 64 among the controls.
“This study clearly shows that HPV screening is more sensitive to picking up precancerous lesions than the other tests,” Sankaranarayanan says. What’s more, he notes, nearly all women who tested negative for any HPV infection at the outset were free of cancer at the end of the study.
The standard test for cervical cancer is the Papanicolaou test (Pap smear), in which a brushing of the cervix is analyzed to detect any aberrant cell growth. An HPV test uses a similar technique but checks for viral infection.
Pap smears require visits at least every three to five years to catch any new aberrant cell growth. This regimen can be difficult to maintain for women in poor countries, Schiffman says. The HPV screening test requires fewer visits, he says.
The HPV test is less likely to help women under age 30 because they get re-infected more often. But a vaccine called Gardasil can prevent infection by cancer-causing HPV types. Even so, vaccination might come too late for women who have already entered the risk pool for HPV, which is spread by sexual contact.
In industrialized countries, the Pap smear is likely to remain the most common test for the time being, Schiffman says. In low-income countries, he envisions a two-tier approach to wiping out cervical cancer. “Vaccinating the girls and screening their mothers would be ideal,” he says.