BBC Three documentary on oral sex and cancer

Image © BBC

Last night’s BBC Three documentary, presented by actress Jaime Winstone, discusses the newest potential cause of cancer – oral sex.

But before you declare a life of celibacy or start railing against those fun-killing scientists, we want to clarify exactly what we do and don’t know on this topic.

The reality is that there are still many pieces missing from the puzzle.

HPV and oral cancer

Oral cancer (also known as mouth cancer) rarely hits the headlines. People traditionally think of it as a disease that affects smokers and heavy drinkers in later life. But over recent years, as oral cancer rates have been increasing , so too has evidence for a new cause of the disease.

We now know that certain strains of a common virus called human papillomavirus (HPV) can also cause oral cancer, alongside tobacco, alcohol, betel quid and a poor diet.

We normally talk about HPV in the context of cervical cancer, and it is the main cause of this disease. But the virus can infect other areas of our body. Spread by skin-to-skin contact, not just by sex, HPV affects almost everyone at some stage in their life.

But there’s no need for undue alarm. In most of us, our immune system fights it off and it doesn’t do any harm. But on rare occasions, the virus takes hold, leading to a chain of events that ends in cancer of the cervix, penis, anus, vagina or mouth.

We know that around fifteen strains of HPV can cause cervical cancer, and that the most common of these – HPV-16 – can also cause oral cancer. But we don’t know how often HPV infections lead to oral cancer, nor how the virus ends up in the mouth.

Oral cancer on the increase

Oral cancer – which includes cancers of the lip, tongue, gums, tonsils and parts of the throat – has been on the increase for about thirty years. In 2009, we highlighted oral cancer as one of the fastest rising cancers in the UK, now affecting around  5000 people each year.

Rates of a certain type of oral cancer – cancer of the tonsil – seem to have been rising especially rapidly. According to the latest statistics, there are around 1,100 cases of these cancers every year in the UK.

Scientists agree that many of these tonsil cancers are linked with HPV. But they aren’t sure exactly how many are related to the virus, and estimates vary from 15 to 85%, depending on the smoking rates in the study population.

This isn’t all bad news. For some reason, oral cancer patients tend to have better outcomes when their tumours test positive for HPV. At the moment, we don’t know why this is.

How does HPV end up in the mouth?

A few case-control studies have suggested that oral sex may be the main way that HPV ends up in the mouth. One of the largest and best of these studies found that people who had more than six oral sex partners, or more than 26 vaginal sex partners in their lifetime had an increased risk of oral cancer.

But the authors of the this US study themselves concluded

Our data suggest that oral HPV is sexually acquired… but we cannot rule out transmission through direct mouth-to-mouth contact, or through other means.

Indeed one study of around 200 college-age men found that those who had more ‘open-mouth kissing partners’ had a higher risk of getting an oral HPV infection.

But these studies about oral sex or kissing have been small, and their results are not conclusive. Up to now, all of the studies on this topic have been ‘case-control studies’. This means that they asked people who had already been diagnosed with oral cancer about their sexual behaviour, often many years ago. This could mean that their responses aren’t entirely reliable. Where possible scientists prefer to ask about behaviours in a large group of healthy people, and then look at cancer rates in this group years later (these are known as ‘prospective studies’).

The HPV vaccine and oral cancer

The BBC’s documentary raised the issue of the HPV vaccination and oral cancer. The HPV vaccine protects against two high-risk strains of HPV (16 and 18). It is very effective at preventing cervical cancer and it is already being offered to teenage girls at school.

Some scientists argue that boys should be vaccinated too. High-risk strains of HPV do indeed cause penile and anal cancers in men as well as cervical cancer in women. But studies suggest that, overall, vaccinating males wouldn’t be an effective use of NHS resources, as long as enough women agree to have the vaccine.

If the vaccine also protects against oral cancer, that could change things. But it’s too early to jump to that conclusion because scientists don’t know yet whether the vaccine could prevent HPV infection in the mouth.

So where does that leave us?

Certainly oral cancer is on the increase, and HPV appears to be playing a role. But there are still a lot of unanswered questions about oral sex, human papillomavirus and oral cancer.  For example, we still need to find out:

• How exactly do people contract HPV infections in their mouths, and how does that affect their risk of mouth cancer? We need large studies to answer this question.
• How common are oral HPV infections in the UK? What happens to these infections? How many of them clear up by themselves and how many persist?
• How long does it take for an infection to lead to oral cancer? And in the meantime, are these signs that doctors and dentists could look for to help screen for the disease?
• Is the HPV vaccine effective against oral HPV infections? Does this affect decisions about the age at which girls are vaccinated and whether boys should be vaccinated too?

Scientists from across the world, including many funded by Cancer Research UK, are working hard to answer them.

Hazel

Hazel Nunn is a senior health information manager at Cancer Research UK