Human Papillomavirus Infection And Cancer Risk
IRA FLATOW, host:
This is SCIENCE FRIDAY. I'm Ira Flatow.
Up first, a look at some new research on HPV infections, human papillomavirus. It's actually a group of viruses, and more than 100 types. And some of these types - HPV 16, for example - have been linked to cancer and other diseases.
HPV can cause cervical cancer, and some types of oral cancer might also be caused by a strain of HPV, which makes new research - just released - so disturbing.
About half of the men in the U.S., Mexico and Brazil - about half the men - are infected with some form of HPV, says a newly released paper in the Lancet, and that's what we're going to be talking about this hour.
Our number is 1-800-989-8255. You can tweet us, @scifri, @-S-C-I-F-R-I.
Dr. Maura Gillison is a professor and the Jeg Coughlin Chair of Cancer Research at the Ohio State University in Columbus. Thanks for talking with us today, Dr. Gillison.
Dr. MAURA GILLISON (Ohio State University): Good afternoon. Thanks for having me on the show.
FLATOW: You're welcome. Anna Giuliano is program leader in cancer epidemiology at the H. Lee Moffitt Cancer Center and Research Institute in Tampa, Florida. I should point out that Dr. Giuliano has received grant money from the Merck Pharmaceutical Company to study HPV, and Merck, of course, makes the HPV vaccine Gardasil. Welcome to SCIENCE FRIDAY, Dr. Giuliano.
Dr. ANNA GIULIANO (H. Lee Moffitt Cancer Center and Research Institute): Thank you very much.
FLATOW: Dr. Gillison, let's start out with some definitions. What is HPV? It's not just one virus, right?
Dr. GILLISON: That's true. HPV is a group of viruses. There are approximately 100 of them that infect humans. Some of the types cause very simple things, like the common wart on the hand or the plantar wart on the foot. But most of the cancer-causing types that we're talking about infect, largely, the genital mucosa and the oral cavity.
FLATOW: And let's talk about these viruses that do that, cervical -there's a cervical cancer, and other genital cancers in men.
Dr. GILLISON: That's true. There are several types that are associated with cervical cancer. The most common one is HPV-16 and HPV-18. And those are both included in the currently available HPV vaccines.
HPV is associated with several cancers that occur in both men and women. In women, it's cervical cancer, vulvar, vaginal, anal cancer and oral cancer. And in men it's penile cancer, anal cancer and oral cancer.
FLATOW: And what is the link between HPV and oral cancer? How close is that link?
Dr. GILLISON: Well, it was declared by the World Health Organization in 2007 that HPV-16 is a cause of oropharynx cancer. Oropharynx cancer is cancer that arises from the back of the mouth or upper part of the throat, most commonly from the tonsil. So in the HPV field, in the head and neck field, it is now established as a cause.
FLATOW: And Dr. Giuliano, you published a paper that looked at the rates of HPV infection in men, and you looked at the genital infection, correct?
Dr. GIULIANO: That's correct. So we were actually detecting 37 different types of HPV occurring - that could occur in men at the external genital skin. And we followed men prospectively so we could actually look at the rate at which men acquire these new infections, and the rate at which these infections are cleared.
FLATOW: And was that a surprising rate: 50 percent of men, Mexico, Brazil, the U.S.?
Dr. GIULIANO: Actually, it wasn't surprising. We had done some smaller studies earlier on in other parts of the United States, and had found very similar prevalence estimates. And in fact, in looking at estimates from other countries around the world, you see, using the same method for detecting HPV, very similar, high levels of HPV prevalence in men at the external genital skin.
But we have to remember: That is a summary measure of all HPV types that were detected.
FLATOW: That's my question. So that doesn't say that all those HPV types cause the cancer.
Dr. GIULIANO: Exactly. And in fact, the evidence that we have is that we can say that one type in particular, and that's HPV-16, is the cause of all of the cancers that Dr. Gillison has just listed for you, that occur in men.
We have very little evidence for other types of HPV causing cancer in men.
FLATOW: Dr. Gillison, is it possible that if you have an HPV genital infection, that you can spread it, or it can be spread to your mouth or to someone else's?
Dr. GILLISON: HPV is a very unusual virus in that it doesn't spread through the bloodstream. So you are correct that a genital infection is considered a distinct infection from an oral infection.
Right now, the principal risk factor for acquiring an oral infection appears to be oral sex, but we can't exclude that you could transmit the infection finger to mouth or even mouth to mouth.
FLATOW: You're saying you cannot exclude that possibility?
No, we can't right now.
FLATOW: Are the incidents of these cancers and the infection rates, are they going up for men and women?
Dr. GILLISON: Well, we know for cervical cancer - because cervical cancer screening is extraordinarily effective - that for the last several decades, incidence rates for cervical cancer have been going down in the U.S.
However, there are cancers for which there is no effective or widely utilized screening program that are caused by HPV, that are going up over time, over the last several decades. These would include vulvar cancer, anal cancer and oral cancer.
For anal cancers, the increase is in men and women. For vulvar cancer, obviously just in women. And for oral cancers, the rate is largely increasing among men.
For instance, since 2000, in the United States, there's been about a 5 percent increase per year among men, and a 10 percent increase in men who are white and under the age of 60.
FLATOW: Is this from having multiple sexual partners?
Dr. GILLISON: We suspect that what is happening is that as a result of the sexual revolution, HPV infection is more common. It only takes sexual contact with one infected partner to acquire an HPV infection. However, the higher the number of partners you've had, the higher the probability that you've been exposed to someone with an infection.
FLATOW: Would condoms be helpful to stop the spread here?
Dr. GILLISON: Consistent use of condoms has been shown to reduce, but not eliminate, infection transmission.
FLATOW: And so what is the take-home message for everybody listening to this, saying: What do I do? What should I do? How do I protect myself? How should I be careful? I'll ask both of you. Dr. Gillison? Dr. Giuliano?
Dr. GILLISON: After you, Anna.
Dr. GIULIANO: OK. Well, I think it's really important to reiterate what Dr. Gillison has just said about screening. We have had very effective cancer-screening programs for the prevention of cervical cancer. So we know that screening can work when we have something available to screen.
The problem that we have for the cancers that are affecting men that are caused by HPV is that we do not have a screening method that we can offer. So we can't prevent those cancers via screening the way we have so effectively with cervical cancer.
So that leaves us with, essentially, primary prevention - which is, how can we prevent infection with HPV? Now, you touched on one method, which is condom use. And as Dr. Gillison said, it's imperfect.
We've published, and others have published, that you get partial protection from condoms, but condom use is important for a variety of reasons. So it's something that we would still strongly promote.
The other is, there is evidence that male circumcision can reduce HPV infection, both in the male as well as transmission to the female partner.
And then the third is, you know, the classic primary prevention through vaccination. And we now have, in the United States, a licensed vaccine against HPV that is available for both males and females.
FLATOW: There's a tweet that came in that says: Please clarify if the HPV study made a distinction between straight and homosexual males, as they have vastly different sexual habits.
Dr. GIULIANO: So in our publication, we assessed both sex with the same-sex partner as well as with a female.
FLATOW: And so it's...
Dr. GIULIANO: And what we find is an increased risk for HPV infections -so acquiring a new infection with increasing number of partners. In the case of men who have sex with men, it's increasing number of male sexual partners, and in the case of men who have sex with women, it's higher risk with an increase in the number of female sex partners.
FLATOW: The fact that this is spreading between men and women is - does the vaccine work in boys as well as girls?
Dr. GILLISON: Well, I'd like to clarify something about the vaccine. We have evidence that the HPV vaccine is effective in preventing anal, genital lesions in women by the HPV types that are included in the HPV vaccine.
Anna just published, also, a beautiful paper in the New England Journal looking at the effectiveness of the vaccine in preventing largely external, genital warts in boys and men, and it was also found to be about 90 percent effective.
With regard to oral HPV and oral HPV infection and cancer or any pre-malignant lesions for HPV-related head and neck cancer, we have absolutely no data. So we can't say that the vaccine has any potential utility in preventing oral infections that lead to cancer because the studies have not been done.
FLATOW: So you're confident of the cancers, but not the oral ones.
Dr. GILLISON: Correct.
FLATOW: Yeah. And just to reiterate my question before - because the audience, I'm sure, is going to be interested - are you, then, recommending that boys get the vaccine also?
Dr. GILLISON: Certainly, there's a permissive recommendation that parents and pediatricians talk about vaccinating boys, largely to prevent genital warts.
I'm advocating, actually, trying to study the use of the vaccine as to whether or not it prevents oral infection.
Dr. GIULIANO: If I can add to that: So there is FDA licensure now for several end points in men. So FDA has licensed the vaccine for the use of the prevention of genital warts in both males and females, as well as anal infection and anal cancer in both males and females.
So we're seeing, as more research is being conducted, we're really seeing an expansion of the utility of this vaccine for both males and females.
And Maura is completely correct. We need to see the efficacy of this vaccine in preventing oral infections and oral disease.
FLATOW: All right, we're going to have to stop it there. Thank you, doctors, for taking time to be with us.
Dr. GILLISON: Thank you, and I just wanted to disclose that I, as Anna, have - I have received funding from Merck.
FLATOW: OK. Thank you for that. Anna Giuliano and Maura Gillison, cancer researchers. Stay with us. We'll be right back after this break.
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