WASHINGTON (AP) ― A prolonged sore throat once was considered a cancer worry mainly for smokers and drinkers. Today there’s another risk: A sexually transmitted virus is fueling a rise in oral cancer.

The HPV virus is best known for causing cervical cancer. But it can cause cancer in the upper throat, too, and a new study says HPV-positive tumors now account for a majority of these cases of what is called oropharyngeal cancer.

If that trend continues, that type of oral cancer will become the nation’s main HPV-related cancer within the decade, surpassing cervical cancer, researchers from Ohio State University and the National Cancer Institute report Monday.

“There is an urgency to try to figure out how to prevent this,” says Dr. Amy Chen of the American Cancer Society and Emory University, who wasn’t part of the new research.

While women sometimes get oral cancer caused by the HPV, the risk is greatest and rising among men, researchers reported in the Journal of Clinical Oncology. No one knows why, but it begs the question of whether the vaccine given to girls and young women to protect against cervical cancer also might protect against oral HPV.

HPV vaccination is approved for boys to prevent genital warts and anal cancer, additional problems caused by human papillomavirus. But protection against oral HPV hasn’t been studied in either gender, says Dr. Maura Gillison, a head-and-neck cancer specialist at Ohio State and senior author of the new research. That’s important, because it’s possible to have HPV in one part of the body but not the other, she says.

A spokeswoman for Merck & Co., maker of the HPV vaccine Gardasil, said the company has no plans for an oral cancer study.

Monday’s research was funded by the NCI and Ohio State. Gillison has been a consultant to Merck.

There are nearly 10,000 new cases of oropharyngeal cancer a year, and overall incidence has risen by 28 percent since 1988 even as other types of head-and-neck cancer have been declining.

Tobacco and alcohol have long been the main causes of these tumors, which occur in the tonsils, base of the tongue and upper throat. But over the past few years, studies have shown HPV is playing a role in that rise, probably due to an increase in oral sex even as tobacco use was dropping.

The new study took a closer look, tracking HPV over time by directly testing tumor tissue from 271 patients that had been stored in cancer registries in Hawaii, Iowa and Los Angeles. The proportion that were HPV-positive rose from just 16 percent in the late 1980s to nearly 73 percent by the early 2000s.

Translate that to the overall population, and the researchers concluded that incidence rates of the HPV-positive tumors more than tripled while HPV-negative tumors dropped by half.

Oral cancer has always been a bigger threat to men than women. Gillison says women account for only about 1 in 4 cases, and their incidence is holding steady while men’s is rising. That raises questions about gender differences in sexual behavior or whether oral HPV infection is likely to linger longer in men.

While HPV is the most common sexually transmitted infection, studies show women’s bodies usually clear the virus from the cervix quickly; only an infection that persists for years is a cancer risk. It’s not known if oral HPV acts similarly or even is as common.

Nor is it clear if oral sex is the only way it’s transmitted, cautions Dr. Gregory Masters of the American Society for Clinical Oncology, an oncologist at Delaware’s Helen Graham Cancer Center.

Regardless, just over 11,000 cases of cervical cancer will be diagnosed this year, a number that has been dropping steadily thanks to better Pap smears. (It’s too soon to know what difference vaccination will make.) Gillison’s team calculated that annual cases of cervical cancer will drop to 7,700 by 2020 ― compared with about 8,700 cases of HPV-positive oropharyngeal cancer by then, about 7,400 of them in men.

The cancer society’s Chen urged caution about those numbers, saying more data is needed. But she says two things are clear: First, patients with HPV-linked oral tumors have better survival odds than those with other types of this cancer, possibly because they tend to be younger. Studies are beginning to test if they can scale back today’s treatment and thus suffer fewer long-term side effects such as problems with speech and swallowing.

And “just because you’re not a smoker or drinker doesn’t mean you can’t get throat cancer,” Chen says ― so get checked for symptoms like a throat that’s sore for longer than two weeks.