Today I have a post over at the Scientific American Guest Blog on male circumcision and cervical cancer. In the post I discuss several papers on the efficacy of circumcision in reducing cervical cancer risk, the physiology behind how circumcision slows the spread of human papilloma virus, and the arguments against circumcision as a prophylactic.
Recently, while I was getting drinks at a pub with about a dozen or so other biologists, I was involved in a very animated discussion about circumcision -- because that's what biologists argue about when they're drunk, apparently.
"They do it to increase stamina. It desensitizes the penis," said a microbiologist. (There's some evidence to the contrary on the bit about stamina, actually.)
"Actually there are studies that show that circumcision decreases the risk of cervical cancer," added an entomologist.
"I have a foreskin and I'm proud of it. I promise you none of my partners have cervical cancer. I think it has more to do with whether or not they practice good hygiene," said an animal biologist (thanks for sharing that with us, by the way). By this point we were starting to get funny looks from the other patrons, and the conversation dissolved without much consensus as to whether circumcision inherently prevents the spread of HPV and cervical cancer, or if not being circumcised merely compounds the issue of poor hygiene. Being the good scientist I am, I decided to dip into the literature to get to the root of the discussion. For now, let's ignore the debates over whether or not circumcision reduces genital sensitivity or the spread of HIV, although these are certainly important things to consider when deciding whether or not to circumcise your children.
Does male circumcision reduce the risk of cervical cancer in their female partners?
A 2002 paper in the New England Journal of Medicine studied men in Europe, Asia, and Latin America, and found that circumcision was correlated with a decreased risk of penile HPV infection (this correlation is corroborated by a 2009 study in African men), but that there was not a significant correlation between circumcision and incidence of cervical cancer.
When they restricted their dataset to women with only one sexual partner, there was an increased risk of cervical cancer in women whose partners were uncircumcised only if their partner was already considered at high risk for contracting HPV (as determined by age at first intercourse, number of sexual partners, and sex with prostitutes). So, in men who already engage in risky sexual behavior, circumcision does offer an advantage for protecting their partners from cervical cancer.
A more recent paper published this year in The Lancet studied HIV negative men and their partners in Africa, circumcising half of the men immediately and the other half after 2 years. Their female partners were tested for high risk genotypes of HPV that are known to cause cervical cancer at the beginning of the study, as well as 1 year and 2 years afterwards. After controlling for lifestyle variables, the women partnered with men who were circumcised had significantly reduced rates of infection with both low and high risk HPV genotypes. However, the women in this study were overwhelmingly monogamous (only 4% of female participants had more than one sexual partner in the year prior to the study), so the results cannot be extrapolated to women with multiple sexual partners.
How does circumcision offer an advantage in reducing the risk of HPV?
Most of the penis is covered by keratinized epithelium that is typical of most other parts of the body. Keratinized epithelium, which has an outer layer of dead cells called the stratum corneum, offers many advantages for protection against viral infections. It is more durable and less likely to tear, so it offers a physical barrier between pathogens and the inside of the body, as well as various chemical defenses against infection and dead outer layers that are constantly being shed, taking any external pathogens with them. However, the inner foreskin has a mucosal lining that is not keratinized, therefore more prone to minute tearing and infection. This mucosal inner surface is pulled back and exposed during intercourse and made susceptible to the transmission of HPV and other viruses. Circumcision reduces the mucosal surface area, thereby potentially minimizing the interface for abrasion and transmission of viruses.
So then what's the problem here? What are the other viewpoints?
From the letters in response to the 2002 study [PDF]:
"Human papilloma virus causes cervical cancer; the foreskin does not. Safer sex, not circumcision, prevents the spread of HPV," says George Hill of Doctors Opposing Circumcision.
"Because infants are not sexually active, they should not be required to bear the burden of preventing sexually transmitted infections. Sexually transmitted diseases will be prevented by practising safer sex, not by circumcising infants. If circumcision is touted as a prophylactic, it could confer a false sense of security and encourage high-risk sexual behavior," writes Arif Bhimji and Dennis Harrison of the Association for Genital Integrity.
While there is evidence to show that circumcision offers an advantage in preventing cervical cancer, it is by no means a cure. The number of sexual partners that individuals may have is a confounding variable, as increased partners or risky sexual behaviors result in an increased incidence in HPV and cervical cancer across all groups. In addition, while it is true that women with circumcised partners are less likely to get cervical cancer, they are not immune. Women with circumcised partners still contract HPV and develop cervical cancer! They just do it at a reduced rate. There are other methods that are much more likely to reduce a woman's chance of contracting HPV and developing cervical cancer, such as vaccination and condom use. Therefore, from a public health standpoint in the United States, it may not be necessary to circumcise male babies solely for the purpose of reducing the risk of cervical cancer in his future sexual partners (of course, this doesn't take into account the possibility that the child might not be heterosexual). This would also be true in similar societies where there is sufficient access to education on safe sexual practices, condoms, and HPV vaccinations. However, the decision whether or not to circumcise a child is a complex one involving cultural, religious, health, and geographic variables, just to name a few.
As for my friend the animal biologist, I shared these papers with him and he came to the same conclusion that I did (though in slightly more colorful language). As long as you and your partner are willing and able to practice safe sex, an uncircumcised penis isn't any more likely to give you cervical cancer than a circumcised one.
Originally published by Scientific American, Inc.
Castellsagué, X., Bosch, F., Muñoz, N., Meijer, C., Shah, K., de Sanjosé, S., Eluf-Neto, J., Ngelangel, C., Chichareon, S., Smith, J., Herrero, R., Moreno, V., & Franceschi, S. (2002). Male Circumcision, Penile Human Papillomavirus Infection, and Cervical Cancer in Female Partners New England Journal of Medicine, 346 (15), 1105-1112 DOI: 10.1056/NEJMoa011688
Wawer, M., Tobian, A., Kigozi, G., Kong, X., Gravitt, P., Serwadda, D., Nalugoda, F., Makumbi, F., Ssempiija, V., Sewankambo, N., Watya, S., Eaton, K., Oliver, A., Chen, M., Reynolds, S., Quinn, T., & Gray, R. (2011). Effect of circumcision of HIV-negative men on transmission of human papillomavirus to HIV-negative women: a randomised trial in Rakai, Uganda The Lancet, 377 (9761), 209-218 DOI: 10.1016/S0140-6736(10)61967-8
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