WEDNESDAY, Feb. 5, 2003 (HealthDayNews) -- A new study may help tweak the development of tailor-made vaccines against cervical cancer by identifying 18 strains of a sexually transmitted virus that causes most cases of the disease.
Researchers have identified 18 types of human papillomavirus (HPV) that have been linked to cervical cancer. While most of the types were already known, three more have been added to the list of "probable" carcinogens.
The results appear in the Feb. 6 issue of The New England Journal of Medicine.
"This codifies what's been the clinical practice in Western countries for at least five years with worldwide justification," says Dr. Giuseppe Del Priore, assistant director of gynecologic oncology at New York University Medical Center and director of the Cancer and Fertility Society. "It estimates the risk perhaps more precisely."
The authors revisit 11 existing studies, the results of which have already been incorporated into clinical practice, Del Priore says.
Virtually all cases of cervical cancer are caused by HPV, which is sexually transmitted. While more than 80 types of HPV have been identified, only 30 or so have been linked with malignancies. According to an accompanying article by Dr. Thomas Wright of Columbia University College of Physicians and Surgeons, the vast majority of cervical carcinomas contain one of 18 types of HPV DNA, as shown in this report.
Cervical cancer is the second most common cancer in women worldwide and the main cancer afflicting women in most developing countries.
In 1995, the International Agency for Research on Cancer (IARC) ruled that there was enough evidence to classify HPV types 16 and 18 as carcinogenic. Last November, researchers announced that a vaccine appears to be highly effective against HPV 16, which accounts for about 50 percent of all cervical cancer cases.
When the IARC made its conclusions, data on other types of HPV were limited, the study authors say. Seven additional studies have been completed since then, giving researchers enough information to draw additional conclusions.
Here, the study authors pooled data from those seven studies, in addition to the four earlier ones that had formed the basis of the IARC's 1995 announcement. These 11 studies came from nine countries and involved 1,918 women with confirmed cervical cancer as well as 1,928 women without cervical cancer.
HPV DNA was detected in almost 91 percent of the women with cancer and in slightly more than 13 percent of the control women. The most common types of HPV in the women with cancer, in descending order of frequency, were 16, 18, 45, 31, 33, 52, 58 and 35.
Among the control women, the most frequent types were 16, 18, 45, 31, 6, 58, 35 and 33.
Based on this information, 15 types of HPV were classified as high-risk. They were 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 73 and 82.
Three types -- 26, 53, and 66 -- were classified as probable high-risk types. Twelve were categorized as low-risk.
Eight types -- 16, 18, 45, 31, 33, 52, 58 and 35 -- accounted for 95 percent of the cervical cancers seen in the 11 studies.
"[These findings] imply that an effective vaccine against the five most common HPV types could prevent about 90 percent of the cases of cervical cancer worldwide," the authors write. Vaccines catering to specific geographical regions would have to take into account differences in the distribution of HPV.
Commercial tests already look for most of these strains, Del Priore says. The ones that aren't included represent such a small number of total cases that adding them into the mix probably wouldn't be worth it.
The study points out that the Hybrid Capture II test hunts for all the high-risk HPV types except 26, 53, 66, 73 and 82. Still, according to the study, in this sample of women, the test would have missed only 1.1 percent of infections in the group of patients with cancer and 0.4 percent in the control group.
"It's really nothing we're going to change practice on. It's a miniscule change," Del Priore says.
The key to cervical health is prevention. Women should make sure they get screened regularly.
More information
For more on cervical cancer, visit the National Cervical Cancer Coalition, the National Cancer Institute or the American Cancer Society.
