Oct. 15, 2008  -- Teresa Dillon was surprised to learn four years ago that what she deemed as an average sore throat actually was stage 2 cancer on her tonsil.

"People think the face of oral cancer is a 70-year-old man who's been chewing tobacco and drinking whiskey all his life," she said. "But the face of oral cancer now is — it's me, a young woman, healthy, nonsmoking, fit."

But what really shocked the waitress and then 38-year-old was that the human papillomavirus may have caused her illness, a illness that is often sexually transmitted.

"It was a virus that caused my tumor, the HPV virus, which just knocked me over," Dillon said.

The HPV Cancer Connection

Dillon is part of a new trend that's puzzling scientists. While most HPV infections clear on their own, there is an alarming surge of oral cancers linked to the virus.

Johns Hopkins researchers reported in a study published in February in the Journal of Clinical Oncology that between 1973 and 2004 the incidence of HPV-related oral cancers among people in their 40s nearly doubled. Today more than 34,000 people have oral cancer and 39 percent of those cases are related to HPV, according to data from the American Cancer Society.

"These are patients that are young. They are in their 30s and 40s. They are nonsmokers, and they don't drink alcohol excessively. And every time we look we are able to find HPV-16 in their tissue, in the biopsy specimen," said Dr. Robert Haddad, a Dana Farber Cancer Institute head and neck surgeon.

High-risk HPV strains cause cancer by using special proteins to disrupt healthy cells. It makes cells unable to repair themselves and unable to control how they are duplicated.

The virus is transmitted by direct contact. You only get HPV in the location it attaches to, so it never travels through the bloodstream.

So just exactly how it gets in the mouth may stun you.

"There is absolutely a link between oral sex and oral cancer," said Dr. Ellen Rome, of the Cleveland Clinic.

Although no proof exists yet, there is a chance that HPV can be transmitted mouth to mouth.

"We can't rule out the virus could be transmitted in saliva by other types of contact — like for instance sharing a drink or sharing a spoon," said Dr. Maura Gillison, of Johns Hopkins Kimmel Cancer Center.

And once the virus is in your mouth, you can't just wash it out. The only way to get rid of it is extensive drug treatment.

HPV Oral Cancer: Who's at Risk?

Men are 35 percent more likely than women to develop HPV-related oral cancer, according to the study in the Journal of Clinical Oncology. But both men and women are susceptible.

While scientists don't know yet how sexual orientation factors into the equation, they know the No. 1 risk factor is a high number of sexual partners. So straight or gay, the more partners, the more risk.

"That doesn't mean it's a magic number. Unfortunately, it only takes exposure to one infected partner to actually acquire the infection," Gillison said.

Infection with the virus usually happens in adolescence. And while oral sex today isn't necessarily more prevalent than it was in the past, it certainly is more accepted. And some often presume it is free of risks.

A 2005 study in the Journal Pediatrics found that teens think oral sex is less risky to their health than vaginal sex.

"I think it's obvious right now to really say that oral sex is not a safe way of having sex and it could have consequences," Haddad said.

"The risks associated with it don't get as much press as the risks you can see with vaginal sex," Rome said. "You don't see someone pregnant after oral sex."

And many don't even know they've contracted HPV and Dillon was one of those people.

"You'd be hard-pressed to find anybody," she said, "who would say that I'm promiscuous, because I'm not."

Dillon, who after six months of grueling chemotherapy is now in remission, said she wishes she had known the risk as a teen.

"You have to be careful. Know who you're with and you have to take precautions. You need to educate yourself. You need to know what's going on," Dillon said.