Circumcision and prostate cancer risk ? correlation is not cause ...

A study published recently by researchers based at the University of Washington reported correlation between circumcision and risk for prostate cancer ? but it is important to note that (a) they were not claiming to have proven a cause and effect relationship and (b) the supposed increase in risk of 15 percent was an increase in relative (as opposed to absolute) risk.

The paper by Wright et al. was published on line today in the journal Cancer. The study is based on self-reported data from 1,754 men who had prostate cancer (?cases?) and 1,645 men who did not (?controls?). The men were asked to provide information about their circumcision status, their age at circumcision, their age at the time of their first sexual intercourse, etc.; this information was then correlated with their history of sexually transmitted infections (STIs) or prostatitis. (Note that some of the information that men were asked to provide, such as numbers of sexual partners, are notoriously inaccurate when people are asked to provide such information 30 years after the events, for all sorts of reasons.)

The study showed the following:

• 1,207/1,754 (68.8 percent) of men who had prostate cancer were circumcised.
• 1,176/1,645 (71.5 percent) of the men who did not have prostate cancer were circumcised.
• Caucasian men were circumcised more commonly than African-American men.
  • 69 percent of Caucasian men reported circumcision
  • Only 43 percent of African-American men reported circumcision.
• 91 percent of the men reporting circumcision stated or implied that the procedure was performed shortly after birth.

Now what this actually means is that men who were circumcised were slightly less likely (in absolute terms) to be diagnosed with prostate cancer than men who were not circumcised. This does indeed translate into a relative risk reduction of 15 percent, and yes, this is a statistically significant difference.

However, it would be a mistake to get the idea that this statistical correlation is necessarily clinically meaningful. There are dozens of reasons why men who do get diagnosed with prostate cancer are more likely to do so that the ?average man in the street.?

Now there are good reasons to believe that circumcision could lower risk for prostate cancer a little. Uncircumcised males are more likely to suffer from sexually transmitted infections than circumcised males. The tissues that make up the inner lining of the foreskin are potentially subject to tearing. Such tears can allow access of pathogens into the bloodstream. To quote the study?s authors, ?The moist environment under the preputial skin may help pathogens survive for extended periods prior to direct infection.? If you cut away this tissue through circumcision, you remove this moist environment.

Next, we know that infections may be the initial cause of some 20% of all cancers ? either directly or indirectly (via inflammation in the latter case). We also know that sexually transmitted infections like chlamydia, gonorrhea, human papillomavirus, and human immunodeficiency virus (HIV) ? have been found in the prostate. But we do not know that infection with any of these infectious agents is actually associated with an increased risk for prostate cancer!

It is probably true that if you are not circumcised, are sexually active from a relatively young age, don?t use protection (not a very good idea in a world where HIV is now common), and are at significant risk for minor tears or abrasions to the preputial tissue, then you may well be at increased? risk for prostate cancer by comparison with your circumcised equivalent. However, the idea that not being circumcised on its own is enough to increase that risk in the post-1980s world of HIV may not be anything like as valid. While we have not seen the full text of the current paper, we have to assume that most of the men in this study would be 55 years of age and older, which implies that a good deal of their early sexual experiences go back to the mid-1970s to mid-1980s or earlier. I?m old enough to know that that really was ?another time.?

Let us conclude by being clear that it is useful to understand that among men diagnosed with prostate cancer there does appear to be this association between circumcision and risk for prostate cancer. However, that is no good reason to think that circumcision today would even reduce, let alone prevent, risk for prostate cancer among a particular male child or group of such children by 2070 or some time thereafter!

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Filed under: Diagnosis, Prevention Tagged: | circumcision, Prevention, risk

Source: http://prostatecancerinfolink.net/2012/03/12/circumcision-and-prostate-cancer-risk-correlation-is-not-cause-and-effect/

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