Tuesday, February 19, 2008

HPV Vaccination: It may not be just for girls

On January 29, I thought I was culminating a discussion of the virus/cancer connection by talking about the link between HPV and cervical cancer, and how the development of a vaccine for HPV could prevent cervical cancer in women.

Shortly after that entry posted, Maura Gillison (a colleague of mine), published an article in the Journal of Clinical Oncology on the growing importance of HPV as a cause of oral cancer. Why is that relevant? One reason is that this represents a shift in the importance of various causes of oral cancer, away from tobacco and towards a virus. This reflects the huge success we’ve had in diminishing tobacco use. As tobacco fades as the leading cause of oral cancer, virus-induced cancer is becoming more common. Interestingly, there is some speculation that this finding might also reflect changes in sexual behavior patterns, especially related to oral sex.

The finding that HPV is now a leading cause of oral cancer means that vaccination of men could significantly impact on the incidence of this disease. So a vaccine (that until now has been given almost exclusively to girls to prevent cervical cancer) could also be given to boys to prevent oral cancer in people of both genders.

The idea of giving the vaccine to boys is not new. This article, from last May, discusses heterosexual sex as the main mode of transmission of HPV to girls, and suggests that vaccinating boys could help break the cycle of sexually transmitted cervical cancer. At the time the article was written, it had recently been discovered that HPV can cause throat cancer, but at that point throat cancer was still more commonly caused by smoking and drinking, so the impact of HPV vaccination on throat cancer was expected to be small.

So what makes Maura’s article a more compelling argument to vaccinate boys is the fact that oral cancer is now more commonly caused by HPV than by tobacco, making the impact of the vaccine greater.

Merck, the manufacturer of Gardisil, the only HPV vaccine available in the US, has been conducting trials of vaccine in boys to determine how tolerable it is. As expected, the vaccine is well tolerated and effective. Effectiveness was measured by determining how many boys who received the vaccination developed antibodies against the virus (almost 100%). There was no difference in effectiveness, measured in this way, between boys and girls.

So… will vaccinating boys have any effect on cervical cancer, oral cancer, or anything else? No one really knows yet. It will be fascinating to watch as these trials are conducted.


Anonymous said...

I'm surprised that the strains covered in the Merck vaccine are the ones that are also responsible for oral cancers. Are they considering including other types as well?

Bruce said...

Dr. Gillison's work is very important. It would seem unlikely that widespread immunization of boys would every be justified given the low incidence of HPV-related oropharyngeal cancer and the cost of the vaccine. Despite this, immunizing girls should still have an impact on the overall incidence in both men and women.

Thanks for a great post!

Doctor David said...

Anon: I think that the same strains cause tumors in both sites because the strains are inherently tumorigenic, and can transform squamous cells regardless of location (though I could be wrong... I'm reaching here... maybe Bruce knows). I don't think Merck is considering other types as well, though I'm pretty sure other companies are, because prevalences vary from place to place, and what works well in the US may or may not work well in Asia.

Great question!

Allen said...

Any thoughts on the recent data regarding side effects of gardasil? I know there are side effects with other vaccinations, but there seems to be a potential for more serious/adverse effects with this one (eg, "700 serious problems such as blood clots and auto immune diseases, and 32 deaths reportedly linked to the vaccine").

Ida said...

I know it's been about 2-3 years since this was posted, but if you still check the comments I'd be grateful for an answer.
I'm a medical student and recently passed my microbiology exam. During microbiology lectures, one of our teachers expressed great distrust in the anti-HPV vaccine. She said that, since HPV doesn't penetrate benieth the stratified epithelial layer, the only antibodies that could possibly protect us were IgA class, who's production could not be induced by parenteral administration of the vaccine. Naturally, none of us students could come up with a good counter-argument and we were tired so we just let the subject drop. But I won't believe the vaccine is no good (I'm vaccined myself, as a matter of fact). Could you please comment on the mechanism of the vaccine's action, or maybe point me in a good direction so I can find out for myself?
Thanks in advance,