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Risk Factor: Throat cancer linked to virus spread by sex

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10:45am, May 9, 2007
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Cancer of the throat and tonsils can arise from infection with a sexually transmitted virus, a new study suggests.

Researchers report that the human papillomavirus (HPV) is much more likely to turn up in the throat cells of people with a malignancy called oropharyngeal cancer than in the throat cells of others. Moreover, the cancer patients were more apt to have engaged in oral sex with multiple partners over past years, suggesting a route of infection, the scientists report in the May 10 New England Journal of Medicine.

HPV infections, which often produce no immediate symptom, were already known to cause cervical cancer. The virus produces localized infections. "It doesn't spread through the bloodstream," says oncologist Maura L. Gillison of Johns Hopkins University in Baltimore. Therefore, an HPV infection acquired through sexual intercourse affects only the genital region, she says, and oral sex may expose the throat and tonsils to a similar viral infection and cancer.

Gillison and her colleagues analyzed throat swabs from 100 people who had oropharyngeal cancer and 200 people without the disease. The cancer patients were 12 times as likely as the others to have an active HPV infection. Moreover, the cancerous cells were 32 times as apt to carry proteins from the viral strain called HPV-16 as were throat cells obtained from healthy individuals.

HPV-16 proteins serve as signs of a past infection by the virus. HPV-16 inserts its DNA into cells that then produce proteins that disable the brakes on cell growth.

HPV-16 is the strain of the virus considered most likely to cause cancer. In a separate test on the same samples, Gillison's team found that HPV-16 DNA showed up in 72 percent of the throat cancers.

Previous work had suggested a biological link between HPV and throat cancer (SN: 4/14/01, p. 229: Infections tied to head and neck cancers). The new study goes a step further by analyzing behaviors that might connect the two. Gillison and her colleagues report that the throat cancer patients were three times as likely as the other people to have had six or more partners on whom they had performed oral sex at some time. And patients whose throat cancers contained the HPV-16 DNA were nearly nine times as apt to have had six or more such sex partners.

"It's worth considering the possibility that some oral, oropharyngeal, and laryngeal cancers might be prevented by HPV vaccination," dentist Stina Syrjänen of the University of Turku in Finland says in the journal issue carrying the new study. Merck is currently marketing a vaccine against HPV under the name Gardasil.

That vaccine is being recommended to protect girls and young women against cervical cancer. The link between HPV and throat cancers suggests that boys, too, might benefit from the vaccine, Gillison says.

The Merck vaccine targets HPV-16 and HPV-18—which cause most cervical cancers—plus HPV-6 and HPV-11, which cause genital warts. GlaxoSmithKline is seeking approval in the United States and Europe for its vaccine Cervarix, which protects against HPV-16, HPV-18, and two other cancer-causing strains.

Two studies also released in the same journal indicate that over several years, the Merck vaccine prevented nearly all precancerous growths in the genital and anal regions of women who hadn't been exposed to HPV-16 and HPV-18 before receiving the inoculations.

However, the vaccine "is not nearly as impressive" for women whose HPV history is unclear, comments gynecologist Karen Smith-McCune of the University of California, San Francisco.

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