A silent epidemic comes into the limelight
Michael Douglas’ revelation of the cause of his cancer has boosted awareness of the risks of the human papillomavirus.
When actor Michael Douglas told the UK’s Guardian newspaper his type of throat cancer was caused by oral sex, he did not just leave interviewer Xan Brooks lost for words. He perplexed a good number of people who thought they knew a thing or two about sexually transmitted infections.
It is common knowledge, especially since the controversy over vaccinating preadolescent girls, that cervical cancer is linked to human papillomavirus (HPV) contracted during sexual intercourse. Thanks to the Hollywood actor, public awareness that the same virus can cause throat cancer has rocketed.
Bucking the general decline seen in the incidence of cancer, throat cancer rates are climbing, most dramatically in middle-aged heterosexual men. Men have always been more at risk than women, linked to their higher rate of smoking and drinking. But even while those habits are declining, the rates of throat cancer are soaring.
According to Cancer Research UK, between 1975 and 2010, throat cancer rates rose 68% in British men. Men now have three times higher lifetime risk than women: 15 in 100,000 compared to five in 100,000.
The answer to the mystery as to why emerged in 2004, when a study from the US National Cancer Institute showed HPV was the culprit. More than 70% of throat cancer is now linked to HPV. It is no surprise that HPV 16 and 18, the viruses that infect the cervix, also infect the throat. The mucous-covered surface of the tonsils and back of the tongue – where Douglas’s walnut-shaped cancer was found – is not unlike the fleshy cervix. The virus also causes penile cancer, anal cancer, and cancers of the vulva and vagina.
But beyond that there are some huge questions. Why has virally caused throat cancer increased – surely neither oral sex nor the virus are new? And why should the virus prefer the throats of men (particularly heterosexual men) to those of women? The first one is relatively easy to answer, says Christopher Fairley, professor of sexual health at the University of Melbourne. What is new, he says is a change in sexual habits.
“Oral sex is more common and at an earlier age. That is consistent with explaining the rise we’re seeing in virus-related throat cancer.” But he is at a loss to explain HPV’s predilection for men. “That is a surprise; we don’t understand why HPV-related cancer is more common in men than women.” So what is to be done? Forget Michael Douglas’ suggestion that “if you have it, cunnilingus is also the best cure for it”.
The good news, reported in July in the journal PLOS One, is that vaccination against HPV 16 and 18 offers strong protection against infection of throat tissue as well as cervical tissue. Of 5,840 Costa Rican women aged 18 to 25 who took part in the study, half were given a Cervarix vaccine against HPV 16/18 and the other half a placebo jab providing no protection against HPV. Four years later, tests showed that of the women given the placebo vaccine, 15 had infected throat cells. Among those who’d received the Cervarix vaccine, just one had a throat infection – a 93% protection rate. The study was “very encouraging”, cancer specialist Eric J. Moore, told The New York Times. “But remember, it only works if you’re vaccinated prior to contracting the infection. Once you’re 40 and have had multiple sexual partners, it’s not going to help.”