Dr. Cathy Popaduik

Tell us about your research

I do research on cervical cancer. My collaborators and I are studying the development of cervical cancer from high risk types of HPV. There are many steps between HPV infection and invasive cancer, and there’s a great deal we don’t know about those steps.

What do people need to know about HPV that they might not already know?

HPV is as frequent as the common cold. We touch it, we share it, we spread it. It’s in every community, region and country. It’s everywhere. Ninety per cent of women will have HPV at some point in their lifetime, most likely when they start having sex. Most will have no issue whatsoever. But if we did nothing, five per cent would go on to develop cervical cancer from high risk HPV.

Simply testing for HPV is not a solution because many women would test positive for it, especially women under 30.  And a single HPV test won’t tell whether the infection is transient or persistent and whether it is causing trouble. The most important thing to understand is that it’s not HPV that we must control, or the behaviours that affect HPV spread.  It’s the deleterious effect of high risk HPV in susceptible people unable to clear it.

What makes the HPV vaccine so important is that it stops the negative effects of HPV in susceptible people by preventing infection of the most common HPV types. That’s our biggest dilemma. How do we identify people who, genetically or immunologically, won’t be able to ward off the bad effects of HPV? For most people, HPV goes through its cell cycle and then goes away. In a small subset of people it gets into their cells, starts mutating, causes pre-cancer, and, in some, it eventually causes cancer.

Recent research in the U.S. and elsewhere has shown that the HPV vaccine works in women, even though not enough women are getting it. Are we seeing the same thing in Canada?

This is exciting research.  Unfortunately, we don’t have the data yet to show the effects of the vaccine in Canada. Over time, we will be able to gather population-based data from provincial vaccination programs. Until then, there’s no reason to believe that the Canadian population will be impacted differently than others.

Expanding HPV vaccination programs to boys has been in the news quite a bit. What are your thoughts on this?

It’s an exciting premise. However, boys and girls respond to HPV differently.  Take seroconversion rates, for example. This is the formation of antibodies in response to exposure to the virus. Boys seroconvert 11 per cent of the time, while girls seroconvert 50 per cent of the time. We don’t know why, and we don’t know the full effects of vaccinating women and how much herd immunity other  non-vaccinated women and men get from it as the beneficial effects of the vaccine spread through a population indirectly.

The microsimulation models that we’ve been using suggest that the positive effects of vaccinating girls are quite striking and will permeate and impact on the male population as well. But you need to consider the value of the small groups that aren’t affected by this. For example, there’s the group of men having sex only with men. How do you make sure they get whatever benefit there is against anal and oropharyngeal cancer?

There is some data showing that men and boys benefit from HPV vaccinations for preventing perianal  pre-cancer and cancer. But those groups are still small and we don’t know enough about the biological impact. For example, a proportion of oropharyngeal cancer appears to be caused by High Risk HPV. Fortunately, oropharyngeal cancer is not as prevalent as, say, lung cancer or prostate cancer, not to say that the people impacted by it aren’t affected tremendously. We do know that about 75 per cent of oropharyngeal cancers from the base of the tongue and the tonsillar area are related to HPV, which is very interesting. But we don’t know the molecular pathogenesis of it yet. In the end, the impact of vaccinating a male directly versus getting the benefit by eradicating the nasty HPVs through the herd immunity from the female vaccination program is still a work in progress.

Ultimately, the vaccine comes at a price, so it’s really up to decision-makers to choose where they want to invest limited dollars. If they want to vaccinate boys, they’re taking money away from a number of new treatments and tests.  It’s a tough decision.

Michael Douglas recently told the Guardian that his throat cancer was caused by HPV. Is this link between HPV and throat cancer something that men need to be aware of? And if so, what can men do about it?

We know that the links with head and neck cancer are primarily smoking and alcohol intake and, more recently, high risk HPV-16. As smoking has decreased, the head and neck cancers that are not attributable to HPV have decreased as well. Those attributable to HPV have increased and tend to happen in people who are 10 years younger than the other non-HPV  head and neck cancers and fortunately people do better with them.

Oropharyngeal cancers happen more commonly in men than in women, but we don’t know why. We really do not have enough data on this yet to make a clear evidence-based conclusion. Anecdotally speaking, I have a patient who within a year of being treated for her locally-advanced cervical cancer was diagnosed with both tonsillar cancer and a metastatic lymph node in her neck. We discovered they were all HPV related and the neck node came from the cervical cancer. I suspect we’re going to see cases of oropharyngeal cancers in women who have been HPV exposed, but on balance men get them more often. What can men do to prevent oropharyngeal cancer? Three things: practice good dental hygiene—dentists diagnose lesions and poor mucosal health can contribute to precancer development—don’t drink and don’t smoke.   The same applies to women.