Chicago - A common virus, believed to be transmitted during oral sex, is the cause of a rare throat cancer in both men and women, US researchers said on Wednesday.
The study is the first to prove the link between the human papillomavirus or HPV - the leading cause of cervical cancer - and oropharyngeal cancer, according to the paper published in the New England Journal of Medicine.
Researchers at Johns Hopkins University, Maryland, who studied 100 men and women newly diagnosed with the rare malignancy and 200 healthy people found that a common strain of HPV - HPV 16 - was present in 72 percent of tumours.
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Patients whose blood or saliva samples indicated that they had prior HPV infection were 32 times more likely to develop oropharnygeal cancer, which affects the throat, tonsils and back of the tongue.
And those people who had had more than six oral sex partners were 8,6 times more likely to develop the HPV-linked cancer.
The figures establish HPV infection as the greatest risk factor for this type of cancer, overturning previous theories blaming a pack-a-day smoking habit for 20 years, or regular heavy alcohol consumption over 15 years.
"It is important for health care providers to know that people without the traditional risk factors of tobacco and alcohol can nevertheless be at risk for oropharyngeal cancer," said Gypsyamber D'Souza, a co-author and assistant scientist.
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.
"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," said study author Maura Gillison.
Scientists are still puzzled as to why some people shrug the virus off, while others get sick from it, but they say that there is good reason to believe the virus is transmitted through oral sex.
HPV can be found in saliva, semen and urine, but has a particular affinity for the mucosal skin cells of the penis and vagina.
Oral cancers linked to HPV have been on the rise in the United States since 1973, a trend that may be driven in part by the popularity of oral sex among American teens, the authors said.
In the light of the increasing incidence of the cancer, authorities should consider programs to vaccinate boys as well as girls against some of the most dangerous strains of HPV, the authors wrote.
Another study published in the journal Wednesday, showed that the first vaccine against cervical cancer, which went on the market in 2006, has proved nearly 100 percent effective.
The vaccine, known as Gardasil, developed by Merck and Company was tested in a large clinical trials of 12 000 women aged 15 to 26, who had not been infected by HPV, and were followed for three years.
Half the group, in hospitals across 13 countries, were vaccinated, the other half received a placebo.
"These clinical trials have consistent efficacy around 98 percent. And severe reactions to the vaccine appear to be rare," said Dr Kevin Ault, one of the co-authors of the study.
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