Vaccine Could Help Prevent Cervical Cancer
Study documents perfect record against responsible virus
WEDNESDAY, Nov. 20, 2002 (HealthDayNews) -- The likelihood that cervical cancer will become less of a killer has taken a huge step forward.
Researchers report that a vaccine against a virus responsible for half of all cases of the disease, which is the second-leading cause of cancer deaths among women worldwide, has a perfect success rate.
The results appear in tomorrow's issue of The New England Journal of Medicine. Another article in the same issue of the journal, however, reports a lower level of effectiveness for a vaccine against herpes simplex virus type 2 (genital herpes): The vaccine was 73 percent to 74 percent effective for women.
Genital herpes affects one in five women in the United States, but does not lead to cancer.
More than 30 varieties of the human papillomavirus (HPV), on the other hand, do have a clear link to cancer. While most cases of HPV resolve on their own, the remaining ones are responsible for about 98 percent to 99 percent of all cervical cancers, says Dr. Carol Brown, an assistant attending surgeon at Memorial Sloan-Kettering Cancer Center in New York City.
HPV-16, the variety for which the vaccine was created, infects some 20 percent of adults. HPV-16 is also the strain most commonly linked to cancer, and is present in 50 percent of all cervical cancers.
"Cervical cancer offers a unique opportunity for prevention, which you don't have for other cancers," Brown says. "We have a way to identify people at risk. HPV lets you do this."
"I think the vaccine approach is going to be very important in the future," says Dr. Cynthia Krause, a gynecologist at Mount Sinai Medical Center in New York City. "There will always be some cervical cancer that cannot be prevented, but clearly HPV is the cause of most cases."
"The reason this study is exciting is because cervical cancer is happening in unscreened or infrequently screened women," says Dr. Carolyn Runowicz, vice chairwoman of the department of obstetrics and gynecology and director of the gynecologic oncology research program at St. Luke's Roosevelt Hospital in New York City.
Runowicz recalls meeting a 36-year-old mother of eight who had had an abnormal Pap smear years before and never followed up. Pap smears detect unwelcome changes in the cervix. By the time Runowicz saw her, the woman had developed lung cancer, which had spread from her cervix. She died soon after.
"The patient was going in and out of the health-care system with young children. At any one of those encounters someone could have discussed prevention with her [if a vaccine were available]," Runowicz says. "That's why I'm so excited about this study because it opens the door for prevention. There are 4,500 deaths from cervical cancer in this country [every year], and it's mostly the unscreened."
The human papillomavirus was not identified until 1983. Even then, however, only tiny amounts of infectious particles could be detected because of the virus's relatively basic genetic structure.
"HPV only has about 10 genes, so it's a pretty simple little thing even though it causes a heck of a lot of trouble," says Dr. Kevin Ault, a co-author of the study and an assistant professor of obstetrics and gynecology at the University of Iowa Carver College of Medicine in Iowa City. This limited vaccine research until 1991, when scientists created noninfectious duplicates of the papillomavirus that stimulated an immune response.
That breakthrough laid the groundwork for the current trial, which enrolled 2,392 women between the ages of 16 and 23. The women, all of whom had tested negative for the virus, were randomly assigned into one of two groups: one received three doses of the vaccine and the other received a placebo. The final analysis included information from 1,533 women, who were followed for a median of almost 18 months.
The incidence of persistent HPV-16 infection (the kind that doesn't clear on its own) in the placebo group was 3.8 per 100 women-years versus zero per 100 women-years in the vaccine group.
While extremely exciting, the study does have its limitations. "This is a good start, but it certainly is not the definitive story," Brown says. "A lot has to be done before we could see a commercially available vaccine."
For one thing, more women need to be studied. And physicians and patients need to know how long the protection will last and whether a booster will be needed. Another issue is the number of human papillomaviruses which each vaccine can inoculate against. The vaccine under study in this trial looked only at HPV-16; there are about five HPVs that are responsible for the majority of cervical cancers.
According to an editorial accompanying the article, vaccinating women against these five HPVs before they become sexually active should result in an 85 percent reduction in the risks of cancer and a decline of 44 percent to 70 percent in the frequency of abnormal Pap smears attributable to HPV. Deaths due to cervical cancer should decline by 95 percent.
Merck & Co. and other pharmaceutical companies are working on this and other multivalient vaccines (vaccines that would protect against more than one strain of HPV). Ault is hesitant to put a time frame on when such vaccines might be readily available, but he will say that he expects his daughters, now aged 3 and 6, will get the vaccine.
What To Do
The American Social Health Association has information on sexually transmitted diseases.