Studies Support Cervical Cancer Vaccine's Effectiveness in Young Girls
And another trial pinpoints HPV as prime cause of throat cancer
WEDNESDAY, May 9, 2007 (HealthDay News) -- Expanded findings from trials that led to U.S. approval of the cervical cancer vaccine Gardasil find it extremely effective in preventing precancerous lesions of the cervix.
The vaccine prevents infection with four strains of the sexually transmitted human papilloma virus (HPV), the leading cause of cervical cancer.
In two studies involving nearly 18,000 girls and women, Gardasil proved almost 100 percent effective in preventing precancerous cervical lesions linked to those strains.
The new studies also found that Gardasil is much more effective when given to girls or women before they become sexually active -- bolstering current recommendations from the U.S. Centers for Disease Control and Prevention that 11- and 12-year-old girls should routinely receive the vaccine as part of school vaccination efforts.
Moves by states to mandate vaccination of young girls have met with strong opposition from conservatives and some parents. But doctors say the new findings, reported in the May 10 issue of the New England Journal of Medicine, support those state mandates.
"All vaccines are going to work best before you have the disease," explained Dr. Kevin Ault, a co-researcher on one of the trials and an associate professor of gynecology and obstetrics at Emory University in Atlanta.
"There's lots of good, practical reasons to give the vaccine to 11-year-olds," he said, including the fact that they have strong immune systems and are already getting shots against other infectious diseases. "But that's one of the best reasons: that they are unlikely to have gotten the virus at that point," Ault added.
Another study, published in the same issue of the journal, points to a potential new reason for both women and men to worry about HPV: throat cancer. U.S. researchers say the virus -- most likely transmitted through oral sex in this case -- is probably the number one cause of throat malignancies, which affect about 11,000 Americans each year.
HPV's connection to cervical cancer remains the biggest concern, however, since it is the second biggest cause of cancer death among females worldwide, killing an estimated 240,000 women each year. The CDC now estimates that more than 20 million U.S. men and women carry cervical cancer-linked HPV.
In Ault's study, called the FUTURE II trial, researchers at more than a dozen medical centers worldwide tracked the effectiveness of Gardasil in more than 12,000 women aged 15 to 26.
Although genital HPV comes in at least 15 strains, Gardasil aims to prevent infection with four strains -- 6, 11, 16 and 18 -- which together are thought to cause 70 percent of cervical malignancies.
The three-year trial found that three standard doses of vaccine were 98 percent effective in preventing high-grade "dysplasia" -- abnormal, precancerous cell growth -- of the cervix in women with no prior exposure to strains 16 and 18.
Not all dysplastic lesions progress to full-blown cancer, Ault explained, but all cervical cancers will go through this precancerous stage.
He called the study results "reassuring" for those who hope Gardasil can prevent girls and women from ever getting infected with the most highly carcinogenic strains of HPV.
Gardasil was somewhat less impressive when women who had already been exposed to HPV 16 and 18 through sexual activity were included in the analysis. In that case, the vaccine achieved 44 percent efficacy in preventing precancerous lesions, Ault's team said.
Vaccinated women with a prior history of HPV 16 or 18 "had a fairly similar rate of dysplasia as women who did not receive the vaccine," said Dr. George F. Sawaya, an associate professor of obstetrics and gynecology at the University of California, San Francisco, and co-author of a related commentary.
One worry is that with types 16 and 18 eased out of the picture by Gardasil, other HPV strains may somehow fill the gap and trigger dysplasias.
"There's some evidence that that may, in fact, be the case," said Sawaya, who is also director of the Cervical Dysplasia Clinic at San Francisco General Hospital.
A second international study, led by Dr. Suzanne Garland of the University of Melbourne, Australia, echoed the results of the FUTURE II trial. That three-year trial, called FUTURE I, tracked the incidence of genital warts and vulvar, vaginal and cervical cancers or precancerous lesions linked to HPV types 6, 11, 16 and 18. The study included almost 5,500 females aged 16 to 24.
This time, vaccination with Gardasil was 100 percent effective in preventing warts, lesions or cancer in women who had never been exposed to the HPV strains targeted by the vaccine. Efficacy dropped to 20 percent when the researchers included women who had already been infected with at least one of the targeted strains.
Both FUTURE trials -- which were funded by Gardasil's maker, Merck & Co. -- lend support to moves by some U.S. states to mandate the inclusion of the vaccine in school immunization programs.
Some parents have withdrawn their children from immunization efforts, citing safety concerns. But, both of the FUTURE trials have so far turned up little in the way of adverse side effects from the vaccine other than the occasional transient fever or soreness at the inoculation site -- problems that can occur with any shot.
"I would hope that big studies in the New England Journal of Medicine will go a long way to relieving people's fears about safety," Ault said. "There have been 2 million doses [of Gardasil] now given in doctors' offices around the United States and there does not appear to be any big safety issue," he added.
Sawaya was a little more cautious, pointing to the fact that one of the nearly 18,000 women studied did develop a very rare vulvar cancer. "That finding gives me pause," he said. "Although we can't draw conclusions from one case of anything, it raises some awareness that we do need to be cautious."
Parents and conservative groups have also suggested that routine vaccination with Gardasil might boost premarital sex among teen girls. "I think it's just the opposite," Ault said. "Studies have shown that the more teenagers know about risk, the less likely they are to take risks. Just because you put a bicycle helmet on your kid, they don't then go out and play in traffic."
HPV might also prove dangerous for a whole new reason, according to the results of a third study published in the same issue of the journal.
Based on new research, scientists at Johns Hopkins University now believe that HPV is responsible for the vast majority of oropharyngheal (throat) cancers. Individuals would typically contract oral HPV infection through oral sex, they said.
In its study, the Hopkins team examined throat tumors from 100 newly diagnosed patients, comparing them to biopsies from 200 healthy control participants.
They found that oral infection with any of the 37 types of HPV tested boosted odds for throat cancer 12-fold. That far outranks the danger from smoking and drinking, the two risk factors previously thought to be the prime culprits behind throat malignancies.
"The real importance of this study is to make doctors realize that people who do not smoke and drink are still at risk of head and neck cancer," said study author Dr. Maura Gillison, an assistant professor of oncology and epidemiology. Too often, she said, physicians overlook the possibility of cancer in nonsmoking, non-drinking patients with chronic sore throat or an unexplained neck mass.
"That means it can be five, six months before the disease makes it onto the doctor's radar screen," Gillison explained.
So, could an HPV vaccine protect women -- and men -- against throat cancer?
Gillison said it's too early to tell, "but I would certainly hope so. In fact, we are currently in the initial phases of discussing how to look at whether Gardasil could prevent oral HPV infection."
For more on HPV and cervical cancer, visit the U.S. Centers for Disease Control and Prevention.