ATLANTA (AP) -- Doctors have known for some time that a sexually spread virus can cause some types of oral cancer. But actor Michael Douglas' comments on his own throat cancer in a newspaper story Monday threw a spotlight on a subject not often discussed.
And it raises a lot of questions:
—What virus can cause oral cancer?
HPV, the human papillomavirus. It's best known for causing cervical cancer and genital warts. It also can be spread by oral sex, and men are more susceptible than women. It is a growing cause of certain types of oral cancer — those in the upper throat, at the base of the tongue and in the tonsils.
Indeed, studies suggest that HPV can be blamed for 60 to 80 percent of cancers of the upper throat.
—What's the risk of getting oral cancer from performing oral sex?
About 2.5 million Americans are estimated to have oral HPV infections. But only about 14,000 cases of that type of cancer are expected this year, suggesting the risk of developing this cancer is low.
The virus is hard to avoid. As many as 75 percent of sexually active men and women will be infected with it at some point. Most people clear the infection on their own within two years. Some, however, have difficulty ridding themselves of HPV. And in some cases, the virus creeps down through tiny fissures in the base of the tongue or in the tonsils to lodge deep in the tissue.
Those deep-settling infections can become dangerous cancers that often aren't diagnosed until they're at a late stage, experts say.
—What are the symptoms for upper throat cancer?
Symptoms can include a sore throat that doesn't go away, pain or trouble swallowing, a lump in the back of the throat, ear pain and voice changes.
—Men are at greater risk?
Apparently, yes. A small study in Baltimore found men accounted for about 85 percent of recent HPV-related oral cancers, said Dr. Sara Pai, a Johns Hopkins University researcher.
Experts believe men have lower amounts of antibody protection against HPV, she added.
—What should I do if my girlfriend or boyfriend has an HPV infection?
Abstain from oral sex, experts advise, though if you've had sex you likely were already infected. And use condoms during vaginal intercourse.
—How do I know if my partner has an HPV infection?
Usually there aren't symptoms, though there may be genital warts. Or a woman might learn from her gynecological exam that she has it. But there is no such testing for men.
—If a woman had an infection but subsequent tests suggest it's gone, is it safe to have oral sex with her again?
Probably. Bear in mind that if you are her partner, you've probably been exposed already.
The issue is not so much whether or not people are exposed to HPV. Rather, it's that some people develop cancer from exposure and some do not, said Dr. Maura Gillison, an HPV expert at Ohio State University.
—Is there a greater risk from a person who's had many sex partners?
Yes, that's the greatest risk factor. HPV is highly communicable, so it only takes sex with one partner to infect you. But the more partners, the greater the chance you've been exposed, Gillison said.
—Isn't there a vaccine against HPV that's available to males?
Yes, but it's recommended for boys before they first have sex. Experts say it generally doesn't work after someone's already been exposed to HPV. There is some work being done on a therapeutic vaccine against HPV, but such a treatment is believed to be many years away, at best.
—Is the risk for oral cancer greater from tobacco or alcohol?
Tobacco especially has been fingered as the cause of most cancers in the head and neck, including in the voice box and at the front of the tongue. Alcohol is believed to be a contributor, too. But cancers of the upper throat are mainly tied to HPV.
—What happened to Michael Douglas?
In 2010, Douglas announced that after seeking treatment for a very sore throat, he was diagnosed with a tumor at the base of his tongue. Because of the location of the cancer, some experts had wondered if it was related to HPV, but Douglas had a history of smoking and drinking and did not go into detail.
Since then, the 68-year-old Douglas has been free of cancer for more than two years after receiving extensive chemotherapy and has returned to acting. On Monday, The Guardian newspaper in England published an interview Monday in which Douglas said HPV is a cause of the kind of cancer he'd suffered.