Oct. 13, 2010 -- Researchers warn of an ongoing epidemic of oral cancer caused by the sexually transmitted human papillomavirus (HPV).

A study in Stockholm, Sweden, finds that cases of oral cancer -- primarily cancer of the tonsils -- increased sevenfold from 1970 to 2007.

They find that while HPV caused only 54% of oral cancers from 1998-1999, it caused 84% of these cancers in 2006-2007.

"It looks like HPV-positive oral cancers are rising quite sharply in the past 10 years, while HPV-negative oral cancers went down. That is why we say it is an epidemic," study leader Tina Dalianis, MD, PhD, professor of tumor biology at Sweden's Karolinska Institute, tells WebMD.

HPV is a well-known cause of cervical cancer. But researchers have only recently begun to appreciate its role in oral cancer, says HPV-oral cancer expert Gypsyamber D'Souza, PhD, of Johns Hopkins Bloomberg School of Public Health.

"Yes there is a startling increase in the incidence of oropharyngeal cancer, and that increase is being driven by HPV," D'Souza tells WebMD. "But while many experts agree that there's an epidemic rise in HPV-related oral cancer, the cancer remains rare."

The risk of developing oral cancer increases with the lifetime number of oral or vaginal sex partners, but many people with HPV-related oral cancer have five or fewer lifetime sexual partners. Men are more likely to get oral cancer than are women, and people with HPV-related oral cancer tend to be younger than people with non-HPV related oral cancer.

It's becoming clear that oral sex is a factor in the spread of HPV-related oral cancer. Less clear is whether deep kissing can spread the virus. D'Souza says that despite some inconclusive evidence of mouth-to-mouth HPV spread, it's unlikely.

"I did one study to suggest it might be transmitted by deep kissing, but the risk was small -- so I think it is unlikely that HPV is transmitted by French kissing," she says. "People with oral HPV infection should not be concerned about interacting with their loved ones in a normal way. Salivary transmission of HPV is very rare."

Smoking and high alcohol consumption are risk factors for non-HPV-related oral cancer. People who smoke also have worse outcomes if they get HPV-related oral cancer.

Oral cancers are extremely deadly, but survival rates are much better for people with HPV-related oral cancer. Because of the high fatality rate for oral cancers, doctors tend to treat them very aggressively. It's not yet clear whether less aggressive therapy might be appropriate for HPV-related oral cancer.

Two vaccines now are approved for prevention of HPV-related cervical cancer. It's not yet known whether the vaccines will protect against oral cancer, but the same HPV types that cause cervical and vulvar cancer cause oral cancer.

"As a virologist, I am not aware of a vaccine that works in one part of the body and not in another, so I think this vaccine would prevent oral cancer in boys as well as in girls," Dalianis says.

The Dalianis study was not funded by pharmaceutical companies. D'Souza reports receiving research grants and consulting fees from Merck, which makes an HPV vaccine.

The Dalianis study appears in the Oct. 13 online issue of the CDC publication Emerging Infectious Diseases.