The human papillomavirus (HPV) is known to cause cervical cancer in women but research from the University of NSW has recently found that it’s implicated in oesophageal cancer, which has been increasing in incidence, especially in men. Norman Swan finds that oral sex, considered a safe option by many young people, may not be as risk free as we think.

When you think about risk factors for cancer, smoking probably comes to mind, maybe obesity and environmental toxins as well. But what about infections?

In fact there are a few viruses that are common causes of cancer. HIV increases the risk of several tumours; hepatitis B causes liver cancer. The other prominent cancer germ is the human papillomavirus (HPV). It causes cervical cancer in women but there’s increasing evidence that it’s a problem for men too.

Research from the University of NSW has recently found that it’s implicated in oesophageal cancer, which has been increasing in incidence, especially in men. Until now no-one’s been sure why.

Professor Shan Rajendra of the Ingham Institute has done a study looking at the various stages leading to oesophageal cancer. It’s already known that having acid reflux is a risk factor (that’s heartburn often with acid going up into the throat), and there’s quite an industry these days around endoscopies for reflux patients. Experts have believed that Barrett’s oesophagus—where the lining of the oesophagus has changed because of the acid assault—commonly precedes oesophageal cancer.

HPV quote When we compare the behaviours of people with oropharynx cancers to those who do not have oropharynx cancer the single greatest difference is oral sexual behaviour, and as the number of partners increases, the risk of cancer increases.

But in fact research suggests that’s quite rare. Most people with this response to the acid never develop a malignancy. So there’s a mystery, which may now have an explanation thanks to this research.

Professor Rajendra’s team have found that a high proportion of those who progress to cancer have HPV in the oesophageal tissue. It still doesn’t prove cause and effect but is a startling finding that could in the future imply that only people with HPV in their Barrett’s need to be followed up. It also could mean, now that boys are being immunised against some forms of HPV, that the incidence of oesophageal cancer will fall in about 20 years from now.

Then there are cancers of the mouth and throat (oropharynx) in men which appear to be growing more common and are strongly related to HPV—as well as smoking.

I covered the situation in the US a couple of years ago. Maura Gillison, Professor of Internal Medicine at Ohio State University in Columbus, claims that oropharynx cancers are rising in incidence in several regions in the world including the United States, Canada, the United Kingdom, Scandinavia, Denmark and Australia among other countries. Data from Sweden suggests this increase can be attributable to HPV, given that tumours that were analysed from the 70s had only 23% positive for HPV. By the mid 2000s that had increased to 93%. In addition, cancer registries in Scandinavia have specimen banks where a large proportion of the population have donated serum. They looked at individuals who eventually developed oropharynx cancer and those who did not and looked back at serum that was collected on average 10 years before. And what they found was that individuals who had antibody HPV 16 in their blood had a 14-fold increase in their risk for subsequent development of oropharynx cancer.

According to Professor Gillison, when we compare the behaviours of people with oropharynx cancers to those who do not have oropharynx cancer the single greatest difference is oral sexual behaviour, and as the number of partners increases, the risk of cancer increases. We also know now from five cross-sectional studies of oral HPV in healthy individuals that when you compare people who have an oral HPV infection to those who do not, that the single greatest factor associated with having an oral infection is the number of partners on whom a person has performed oral sex, and that the risk increases as the number of partners increases.

This relationship between HPV and head and neck cancer is relatively new so there’s lots of catching up to do. The cervical cancer field is about 20 years ahead and whereas the natural history studies of cervical infection clearly linking behaviour to acquiring infection (and then developing a pre-cancer) were done many years ago, similar studies of the oropharynx are in their infancy.

But we do know that the rise in oropharynx cancer in the US is predominantly among young white males.

Bonnie Halpern-Felsher, who's Professor of Adolescent Medicine at the University of California San Francisco, says that young people’s sexual habits could be catching up with them later. It’s likely that—like cervical cancer—it takes a few years for a human papillomavirus infection to induce a malignancy in the mouth, tonsils or throat.

For the past 10 years Professor Halpern-Felsher’s group have been following a sample of just over 600 adolescents, assessing them twice a year through high school and looking at three specific questions.

Firstly, what are the perceptions and attitudes that adolescents hold about oral sex? What role do those play in their decision-making and how do those perceptions compare to vaginal sex?

Secondly, what are the experiences that adolescents are reporting that they have when they have oral sex?

And finally, is there any relationship between teens' engagement in oral sex and subsequent vaginal sexual behaviour?

What they’ve found is that adolescents do think that oral sex is less risky when it comes to health risks such as STIs and certainly pregnancy. They also perceive that oral sex is less risky when it comes to social and emotional risks—basically they feel that it's not that big of a deal for them to have oral sex.

Adolescents who had oral sex compared to vaginal sex were also experiencing less health, social and emotional consequences. (They also reported experiencing fewer positive benefits... such as pleasure).

Finally they found that adolescents who had oral sex in 9th grade and early 10th grade were significantly more likely to go on to have vaginal sex in high school. So oral sex seemed to be predicting or speeding up the chances of having vaginal sex.

Luckily the current HPV vaccines cover the common types of the virus seen in the mouth and throat so it’s good that boys in Australia are now being immunised.

It's reasonable to extrapolate and to hope that the vaccine could reduce the incidence of oropharynx and oesophageal cancer but we don’t know that for sure yet.

Interestingly, circumcision has been shown to reduce transmission to partners. An individual who is not circumcised has higher HPV prevalence.

Cigarette smoking is still a major risk factor for head and neck cancers worldwide but as smoking rates decrease in developed countries like the US and Australia, HPV is taking over.

So just when you thought it was safe to go out, along comes another risk to mug you.

Dr Norman Swan presents the Health Report where you can download this story as a podcast.