“Men who have performed oral sex on five or more women are at greater risk of developing head and neck cancer, especially if they smoke,” the Evening Standard reports.
This story is based on a US study that looked at 9,425 people aged 20 to 59 who provided information about their number of oral sex partners and were tested for oral human papilloma virus (HPV).
HPV is a virus that can infect moist membranes. Certain strains can increase the risk of cervical cancer in women, and if particular strains are found in the mouth, this may increase risk of mouth and throat cancers. The virus can also cause genital warts.
The researchers found that 6% of men and 1% of women carried potentially cancer-causing strains of HPV in their mouth. They noted that this was more common in smokers and in men with an increased number of oral sex partners. However, the study can`t prove causation and is not precise enough to link a specific number of partners with risk of carrying oral HPV – or of cancer.
They also looked at registry data to see how common mouth and throat cancers were in people carrying these harmful oral HPV strains and found that it is still very rare: estimated at 7 in 1,000 men and 2 in 1,000 women.
Therefore people shouldn’t be too concerned by these findings – but that doesn`t make it any less important to practise safe sex. If you are concerned about potential risk from oral sex, use a dental dam – a piece of latex that covers the vagina and anus and protects you against a range of sexually transmitted infections.
Where did the story come from?
The study was carried out by researchers from Johns Hopkins University and Information Management Services, Inc., both in the US. It was funded by the National Institute of Dental and Craniofacial Research. It was published in the peer-reviewed medical journal Annals of Oncology, and the article is free to read online.
The UK media`s headlines for this story were generally misleading. The research looked at a range of risk factors but the headlines focused mostly on oral sex. Many gave the impression that a direct link had been identified between a specific number of sexual partners and getting cancer.
The research actually looked at the effect the number of partners had on how common the cancer-causing oral HPV was and made predictions about cancer risk from other data. Most articles clarified this point further down, but may have confused people.
Arguably the fact that smoking particularly increased the risk of HPV-associated cancers could have been made more prominent in some of the reporting.
Many articles also referred to this as `head and neck cancer`, when the study actually looked at cancers of the mouth and throat.
What kind of research was this?
This was a cross-sectional study using national survey data, where people were assessed at a single point of time to look at their health and behaviour, cancer registry data was also used.
The researchers wanted to see how common oral HPV infection was, and whether particular groups of people had a higher risk of being infected, which could possibly increase their risk of mouth and throat cancers. They were interested in finding out whether screening for oral HPV might be a useful thing to do in the general population as a cancer detection strategy.
Although cross-sectional studies can be a useful way of finding out a lot of information about a large number of people, they don`t give us the chance to see how things happen over time. So we cannot know how long people with HPV had been infected for, or whether any of them actually went on to develop cancer – the study can only suggest links.
A cohort study that followed individuals over time and looked at cancer development could better investigate these questions, but this is not likely to be practical as mouth and throat cancers are quite rare. You would need a very large cohort population to produce any meaningful data.
What did the research involve?
The researchers used data collected by the National Health and Nutrition Examination Survey (NHANES) from 2009 to 2014. They included 9,425 people aged 20 to 59 who provided information about their number of oral sex partners and were tested for oral HPV.
HPV testing was carried out by providing an oral rinse and asking participants to gargle. Laboratory methods were then used to detect HPV DNA in these mouth rinse samples. The researchers recorded the presence of any strains of oral HPV that had been identified as harmful.
The researchers analysed the relationship between prevalence of oral HPV and different risk factors, including age, sex, ethnicity, sexual behaviours and smoking habits.
They gathered data on the number of mouth and throat cancers from the Surveillance, Epidemiology, and End Results (SEER 18) registries, which cover about a quarter of the US population. They also used the National Center for Health Statistics (NCHS) to look at deaths from these cancers.
They used this combined information to predict risk of mouth and throat cancers from cancer-causing HPV in oral rinse samples.
What were the basic results?
The researchers found that infection with cancer-causing oral HPV was not that common, but that some groups were at higher risk of being infected than others:
- men were more likely to be infected than women (6.0% versus 1.1%)
- current smokers were more likely to be infected than non-smokers (6.7% versus 2.6%)
- there was a trend of increasing risk of infection as the number of oral sex partners increased (10 or more partners: 11.1% risk; 5-9 partners: 3.3% risk; 2-4 partners: 2.5% risk; 1 partner: 1.1% risk; 0 partners: 1.2% risk)
When the researchers looked at existing data on risk of mouth and throat cancers among people who were infected by these harmful oral HPV strains they noted that, over the course of a lifetime, only two in 1,000 women and seven in 1,000 men were likely to develop these cancers.
How did the researchers interpret the results?
The researchers concluded that cancer-causing oral HPV isn`t that common in the general population, which means that carrying out whole-population screening would not be useful in cancer prevention.
However, they noted that mouth and throat cancers were becoming more common, and that it would be useful to identify people at higher risk of these, including people who have a high risk of getting an oral HPV infection. Nonetheless, they noted that even these high-risk people still have a low risk of developing mouth and throat cancers.
This study uses a large amount of national data to give us an idea about which groups of people have the greatest risk of carrying potentially cancer-causing oral HPV.
But while oral HPV may increase people`s risk of mouth and throat cancers, the actual number who would go on to develop cancer is extremely small.
This study has limitations, which are worth bearing in mind:
- It only looked at whether people had oral HPV at a single point in time. This makes it difficult to know at what point they became infected and how much this could be down to other risk factors such as smoking, oral sex and number of partners. The researchers were only able to make predictions about likelihood of going on to develop cancer once infected. We cannot put a definite number to this risk.
- The study only looked at US data. Though risk of HPV infection and of mouth and throat cancer is likely to be similar, we cannot directly apply these findings to the UK.
It is always sensible to practise safe sex to reduce your risk of getting a sexually transmitted infection. If you are concerned about getting HPV or any other type of STIs through oral sex, use a condom or dental dam.
A vaccine against some strains of HPV is offered to girls aged 12 to 13 as part of the NHS routine vaccination schedule.
Currently, any males wanting the vaccine will have to pay for it. The course of three injections costs around £400 at the time of writing.