Professor Margaret Stanley, Dept. of Pathology, Cambridge University
Kat - Thereís lots of ways and reasons that cancer develops, but in some cases, we do know that viruses can cause the disease and the human papillomavirus or HPV is the main cause of the majority of cases of cervical cancer. And today, weíre joined in the studio by Professor Margaret Stanley from the Department of Pathology at Cambridge University. Hello, Margaret.
Margaret - Hi there, Kat.
Kat - Letís talk a little bit about HPV, this virus we hear so much about in the news. How does it actually cause cancer? How does a virus cause cancer?
Margaret - Well the first thing I have to say is that HPV is a huge family of viruses, so weíre only talking about a few members of this family that actually have the ability to cause cancer because they cause lots of other things, but only a few of them cause cancer. How do they do it? Well, the ones that cause cancer actually are pretty decent people on the whole, but in certain circumstances, the way in which the virus is growing in the cells is de-regulated. There are accidents that happen and the virus actually uses the cellís own ability to divide to help it make its own virus particles. But if itís turned on, if certain genes are turned on in cells that really are actively dividing then it makes the cell cycle of those cells completely chaotic. And so, itís an accident that happens, itís a rare accident, but once it happens, the cell is de-regulated, it no longer can control how often it divides, and thatís the way this virus causes cancer Ė accidentally.
Kat - So it effectively hijacks the cell and makes them multiply.
Margaret - Absolutely.
Kat - And weíre talking about lots and lots of different types of HPV. There is only a few that cause cancer. Do they cause other diseases as well?
Margaret - Yes. HPV is not just the cause of cervical cancer. It causes cancer of the vulva in women, cancer of the vagina - only 50% of those cases but it causes cancer of the anus which is the back passage and itís looking as though it causes probably more than 90% of those. And recently, it has become clear it also causes cancer in the mouth. Now itís only special places in the mouth. Itís the back of the mouth, the skin that covers the tonsil and at the base of the tongue. The skin that covers the area there and it looks as though it causes probably 80 to 90% of the cancers in those sites.
Kat - Obviously, we hear about HPV infection. How does someone become infected with HPV?
Margaret - Well, in the genital area, itís a sexually transmitted infection and everybody throws their hands up at this. But I always say itís actually easier to catch HPV than it is to get pregnant. Itís an inevitable part of having a normal sex life. So virtually, all of us are actually being exposed to this virus in our genital area. 80% of us probably will have been infected throughout our lives, but nearly all of us get rid of it. Itís just a small fraction of people who somehow can't get rid of this virus. Their immune system can't do the business.
Kat - So this is the question obviously if many, many thousands, hundreds, millions of people are infected with HPV, but only every year, say 3,000 or 4,000 women get cervical cancer: What is the difference between having an HPV infection and getting cancer and having an HPV infection and not?
Margaret - I wish I knew.
Kat - What are the clues?
Margaret - Well of course, we don't know who is susceptible to HPV infection. We don't know which women and men are totally unable to get rid of it. What we can do of course is identify those people, those women who have not manage to get rid of the virus, and in whom these genetic events that cause cancerous cells are occurring. Thatís why you have cervical smears. So we can identify those people once they've started that process of turning cells into abnormal cells. But I can't go out into the population and say, ďLook, I know you won't be able to get rid of HPV, so I'm going to do something about it.Ē I can't do that.
Kat - Weíre going to hear later a bit more about cervical screening, but letís talk now about the vaccine because obviously, if we can prevent people from getting infected with HPV, we could actually prevent the process of developing cervical cancer at all. How does the vaccine actually work? Whatís it designed for?
Margaret - The vaccine is designed to generate the immune response that would prevent the virus infecting cells. In other words, it generate antibodies and antibodies are things that bind viruses and stop them getting into cells, and if the virus can't get in to a cell, then it can't start the business of changing the cell. So the vaccine generates antibodies in you and it generates antibodies at a good level and probably all sorts of other bits of the immune response. So, you take 13-year-olds which is what we do in this country and we give them the vaccine, and that means that as they grow up through their teens, 20s and 30s, if they are exposed to the virus, the virus can't get into cells because the antibody binds to it and stops it. So thatís how the vaccine works.
Kat - So itís important to protect girls before they become sexually active.
Margaret - Absolutely. Vaccines don't work once you're infected. They only work to stop you getting infected which is the reason why you take adolescents who are at that early stage in their lives, and they havenít started their sexual life.
Kat - You would certainly hope not.
Margaret - I would definitely hope so.
Kat - And how is the vaccination program going so far? What are the early results?
Margaret - Itís been a stunning success. I think itís the only way I can describe it. If you're going to be effective with a vaccine, you probably need to get 80% of people vaccinated. Now, in the couple of years that this vaccination program has been going, on average, between 80% and 90% of 13 year olds in Britain have been vaccinated Ė an absolutely stunning success. Probably the best results in the world.
Kat - Fantastic! So in a few years, we should see a big drop in cervical cancer incidents.
Margaret - Well, initially, weíre going to see a drop in the pre-cancers, the things that you hope are identified by the smears. But I think whatís really important to emphasize is that we will see a drop in young women with cervix cancer Ė people think of cervix cancer as something that you get when you're 40, 50, 60. Actually, in this country, there are about 300 women under 30 every year who get cervical cancer. We ought to see a drop in that in the next 10 years.
Kat - Wow! Weíll look forward to that. Thank you. Thatís Margaret Stanley from Cambridge University, shedding light on the link between HPV and cervical cancer.