The incidence of oral cancer due to a virus transmitted during oral sex has increased steeply over the last 30 years, according to research in the US. And scientists relate this trend to changes in people's sexual behaviour.
The number of tongue, mouth and throat cancers due to the sexually transmitted human papilloma virus (HPV), which can also cause cervical cancer in women, rose by about a third from 1973 to 2004, say researchers.
The team led by Maura Gillison at Johns Hopkins University in Baltimore, Maryland, US, studied trends in oral cancers recorded by US National Cancer Institute registries.
Earlier work by this team and others had established a link between certain strains of the common sexually transmitted virus and oral cancer. The latest study, which looked at nearly 46,000 cases, is the first to quantify an increase in mouth and throat cancers due to sexual activity.
"What we do know is that the prevalence of HPV is high, particularly among young people and this shouldn't be a surprise given that, since the sexual revolution, people have been having more sexual partners," says Lesley Walker, director of cancer information at Cancer Research UK.
The rise was largest among young white males, suggesting this group is more likely to have oral sex at a younger age now than it was 20 years ago, says Gillison's team. It adds that further research on the role of race and sex, and oral sexual behaviour, is needed.
What is not in doubt, says Gillison, is the need to consider giving boys the HPV vaccine, to protect them from the disease.
A Merck vaccine is currently licensed for use in young women and girls to protect them against the most common cervical cancer-causing strains of HPV. These strains are also thought to cause oral cancer, as well as penile and anal cancer.
"We need to start having a discussion about those cancers other than cervical cancer that may be affected in a positive way by the vaccine," urges Gillison.
One US campaign group, the Oral Cancer Foundation, is now calling on the US Food and Drug Administration to "move rapidly to approve the vaccination of young boys with the cervical cancer vaccine, to reduce the pool of HPV16 [a particularly aggressive strain]" and protect them from oral cancer.
Walker says however, given the high cost of such a programme, authorities might require more evidence that such a move really would prevent a significant number of male cancers.
Tonsil and throat cancers affect about two in every 100,000 adults in the US and about half a million people around the world each year.
Although, oral cancers linked to HPV infection have risen, the study notes the incidence of oral cancers in parts of the mouth or throat not linked to HPV infection remained constant until 1982, and then started to decline.