If you're keeping score, here's even more evidence that HPV causes oral, head and neck cancers and that vaccines may be able to prevent it.

Researchers studying the human papillomavirus say that in the United States HPV causes 64 percent of oropharynxl cancers. In the rest of the world, tobacco remains the leading cause of oral cancer, Dr. Maura Gillison of Ohio State University told a meeting of the American Association for the Advancement of Science this past weekend.

And the more oral sex someone has had — and the more partners they've had — the greater their risk of getting these cancers, which grow in the middle part of the throat. "An individual who has six or more lifetime partners — on whom they've performed oral sex – has an eightfold increase in risk compared to someone who has never performed oral sex," she said.

The recent rise in oropharnx cancer is predominantly among young, white men, she noted, though she says no one has figured out why yet. About 37,000 people in the United States were diagnosed with oral cancer in 2010, according to the Oral Cancer Foundation.

People with HPV-related throat cancer are more likely to survive their cancer than those who were heavy smokers or drinkers, the other big risk factors.

The message may be more critical for teens according to Bonnie Halpern-Felsher, professor of pediatrics at the University of California, San Francisco. She has studied 600 adolescents over 10 years and found that oral sex is much more common than vaginal sex and that "teens don't consider oral sex to be sex," that they think "it's not that big a deal." She adds: "Parents and health educators are not talking to teens about oral sex. Period."

Worldwide, HPV-related cancers seem to be increasing. Gillison said that Swedish researchers looking back over 30 years found that 23 percent of oral cancer tumors in 1970 were positive for HPV, but in 2005, that number had risen to 93 percent.

The British newspaper The Guardian noted that Gillison said that "every birth cohort appears to be at greater risk from HPV and oral cancers than the group born before them."

Over the past five years, health officials have been urging parents to make sure their daughters are vaccinated against HPV to help prevent cervical cancer. But these new results suggest that young men could also benefit from vaccination, though the costs would be substantial.

While none of the researchers could say definitively that the vaccines against HPV, Gardasil and Cervarix, would prevent throat cancer, they thought it could was reasonable to think the vaccine could reduce risks as well.

Note: Some of Gillison's research is funded by Merck, the pharmaceutical company that makes Gardasil.

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