A doctor writes: We need to talk about oral sex and cancer

Vaccination rates against the human papilloma virus (HPV) have dropped dramatically as a result of a campaign by so called anti-vaxxers. While their motivation is multi-pronged, it has been suggested that one group, the religious right – especially in the US – have adopted an anti HPV stance in the belief that vaccinating 12- and 13-year-olds (to prevent a sexually transmitted infection) encourages premature sexual activity.

Introduced in the Republic in 2010 on the recommendation of the World Health Organisation, HPV vaccination is primarily aimed at preventing cancer of the cervix. Almost every case of cervical cancer – about 99 per cent – is estimated to be caused by persistent infection with certain strains of HPV.

Less prominent in the global debate about HPV has been its association with oral cancer. Tobacco and alcohol are traditionally seen as the main risk factors for oral cancer but there is now overwhelming evidence that HPV plays a causal role in some types of the disease. For example, Canada, Denmark, the Netherlands, Norway, Sweden, the US and the UK have witnessed increasing incidence of oropharyngeal and oral cavity cancers despite declines in smoking rates since the 1980s.

But this link flew beneath the radar until 2013 when the actor Michael Douglas disclosed in an interview with the Guardian newspaper that his throat cancer was "caused by HPV which actually comes about from cunnilingus".

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As a result, the link between HPV and oral cancer and the transmission of HPV via oral sex received extensive media coverage.

The main risk factors for oral infection with HPV are thought to be a greater number of oral sex partners due to greater exposure to the virus. This is an argument for vaccinating boys as well as girls as a preventive health measure; however the proposal has reinforced the fears of religiously motivated anti-vaxxers.

Despite a temporary surge in interest at the time of the Douglas comment, awareness of the signs and risk factors for head and neck cancer is poor and the majority of oral cancers continue to be diagnosed at an advanced stage. In one US population-based online survey, HPV was recognised as a common risk factor for mouth and throat cancer by fewer than 1 per cent of participants, and even when prompted explicitly about the link, just 13 per cent said they had heard of the association.

Lie dormant

Experts believe HPV may play a part in the development of some oral cancers. It seems the virus can lie dormant for many months or even years before causing cell changes that, in some people, may develop into cancer.

A recent review in the Postgraduate Medical Journal set out to determine whether there is strong evidence to correlate oral sex with head and neck cancers, which in turn would justify sexual behaviour counselling for patients.

The authors report a four times higher prevalence of oro-genital sex in patients with HPV-positive oral cancers than in HPV-negative patients. In addition, a meta-analysis of sexual behaviours and head and neck cancers suggested an increased risk of head and neck cancers among people with a higher number of oral sex partners.

Sexual behaviours like having unprotected oral sex, practising oro-anal sex or having multiple sexual partners play an important role in HPV transmission and infection that may result in HPV-associated head and neck cancer, “which is an emerging epidemic”, they conclude.

“Patients are more likely to be younger, well-educated males from higher socio-economic backgrounds. There is a need for proper documentation and for counselling of patients regarding sexual behaviours to prevent the spread of HPV infection and associated cancers.”

But a couple of important research questions remain to be answered: why do women have a lower incidence of HPV-related oropharyngeal carcinoma?

And which specific sexual behaviours are most likely to lead to HPV transmission?