Published in the May 10 edition of New England Journal of Medicine (NEJM), the study found that having multiple oral sex partners tops the list of sex practices that boosts the risk of HPV-linked cancer, regardless of tobacco or alcohol use.

Researchers from Johns Hopkins University who studied 300 adults found that having six or more oral-sex partners during their lifetime had a nearly nine-fold increased risk of developing cancer of the tonsils or at the base of the tongue.

In Study author and cancer virus expert Maura Gillison's study of 100 men and women newly diagnosed with oropharyngeal cancer (located in the tonsils, back of the tongue, and throat), those who had evidence of prior HPV infection were 32 times more likely to develop the cancer. This was much higher than the rate increase of three-fold for smokers and two-fold for drinkers.

Study participants who reported having more than six oral sex partners in their lifetime were 8.6 times more likely to develop the HPV-linked cancer. In a surprising twist, Gillison says their data show no added risk for HPV carriers who smoke and drink alcohol.

"It's the virus that drives the cancer," explains Gillison, an assistant professor of oncology and epidemiology at Johns Hopkins. "Since HPV has already disrupted the cell enough to steer its change to cancer, then tobacco and alcohol use may have no further impact."

Dr Julie Sharp, science information officer at Cancer Research UK, however has disagreed with some of the findings.

"There is conflicting evidence about the role of HPV, and this rare type of throat cancer. As this was a small study, further research is needed to confirm these observations. We know that after age, the main causes of mouth cancer are smoking or chewing tobacco or betel nut, and drinking too much alcohol."

Gillison added that "people should be reassured that oropharyngeal cancer is relatively uncommon, and the overwhelming majority of people with an oral HPV infection probably will not get throat cancer."

Consistent condom use may reduce risk.

Oral sex, including both fellatio and cunnilingus, is the main mode of transit for oral HPV infection, the investigators say, although mouth-to-mouth transmission remains possible and was not ruled out by the current study.

According to News-medical.net, HPVs also can be transmitted by skin contact and are found in the mucus of the genital tract, and in saliva, urine, and semen. Both men and women contract the ubiquitous virus in equal numbers, which is believed to have infected a large proportion of people worldwide at some point in their lives. Most HPV infections clear with little or no symptoms, but a small percentage of men and women who acquire cancer-causing or "high-risk" strains, such as HPV 16, may develop a cancer. HPV-linked cancers currently include oral, anal, cervical, vaginal, penile, and vulvar cancers.

Gayhealth.com, a resource web site for the lesbian, gay, transgender, and bisexual communities, noted that "the throat cancer study did not explore whether Gardasil, the Merck & Co. HPV vaccine approved by U.S. regulators in June, would be protective against oral infections."

The findings are expected to spur new debate over whether it should be more widely prescribed to boys and men since oral HPV infection occurs in both men and women who engaged in this type of sex. The Advisory Committee on Immunization Practices (ACIP), which advises the US Centers for Disease Control and Prevention, currently recommends for girls and women between 11 to 26 to be vaccinated against the cervical cancer causing virus.