A study of women in Costa Rica is raising hope that getting vaccinated against the human papillomavirus, or HPV, could lower the risk of throat cancers.
The research doesn't show that. It would take a much bigger and longer study to do that – if such a study could ethically be done at all.
What this study does show is that among the nearly 6,000 women in the study, those who got vaccinated against two strains of the virus had 93 percent fewer HPV throat infections four years later.
Since the virus is strongly linked to throat cancers, that should reduce the risk of these malignancies.
If it does, there's no reason to think the vaccine wouldn't lower risk of throat cancer in men, too. But that involves another set of inferences that the new study can only suggest, not support.
Two HPV vaccines are already approved for prevention of cancer of the uterine cervix in women, and prevention of genital warts and anal cancer in men. The study, published in the journal PLoS One, involved one of the vaccines, GlaxoSmithKline's Cervarix. (The other is Merck's Gardasil.)
The questions raised by the study are important ones.
This year more than 41,000 Americans will get a diagnosis of oropharyngeal cancer – affecting the throat, base of the tongue or tonsils. Nearly three-quarters of them are men.
Once cigarette smoking was the main cause of these cancers. But HPV infection is rapidly displacing cigarette smoking as the main culprit. (One relatively bright spot: HPV-caused throat cancers are less lethal than those due to smoking.)
A 2011 study found that HPV-associated throat cancers have increased from 16 to 72 percent of all such malignancies. That shift could reflect a decline in smoking-related throat cancers, an increase in those from oral sex – or both.
"If recent incidence trends continue, the annual number of HPV-positive oropharyngeal cancers is expected to surpass the annual number of cervical cancers by the year 2020," the study's authors said.
Earlier this summer the role of HPV in throat cancer got a big dose of attention when actor Michael Douglas suggested his case was probably caused by HPV acquired through oral sex with women. He later amended that, saying he couldn't know the exact cause.
Heterosexual men appear to be at the same or somewhat higher risk than homosexual men of getting HPV throat infections through oral sex, perhaps because vaginal secretions contain more of the virus than are found on the skin of the penis.
It's hard for sexually active people to avoid HPV infection. Something like 80 million US adults have it, though 90 percent of the time their immune systems clear it over a period of months to years.
For the other 10 percent who get persistent HPV infections, it would clearly be a great boon if the two HPV vaccines already approved turned out to prevent throat cancer, too. But it's going to take more research – and perhaps some creative interpretation of the results – to show it.