The best-established correlates of prostate cancer are advancing age, a family history of prostate cancer, and African ancestry.
In a large case-control study from Washington State, Wright et al. found that, overall, circumcision status was not associated with the presence of prostate cancer. In this study, men circumcised after first sexual intercourse actually had a slightly higher (though non-statistically-significant) rate of prostate cancer than never-circumcised men. Only by combining this group (with its higher risk rate) with the never-circumcised men, were the investigators barely able to reach statistical significance, claiming a small relative risk reduction of 15% for the remaining men who had been circumcised before sexual debut.
Spence et al., using a similar case-control design with a large population in Canada, also found no overall association of circumcision status with prostate cancer rates. When stratifying the results by racial ancestry, the investigators found a reduced rate only for Black men, but not for any other racial groups. Contrary to Wright et al., Spence et al. found a reduced rate of prostate cancer in men circumcised after the age of 35, but no significant difference for any other age group. Both groups of investigators assumed that the control group (men who had never been diagnosed with prostate cancer) did not actually have prostate cancer. In fact, however, prostate cancer has been shown to be present upon autopsy in one-third of undiagnosed men, a factor which could negate any of the above results.
Both of these studies were based on several tenuous assumptions. The first assumption is that the risk of prostate cancer is increased by sexually transmitted infections. However, the medical literature is mixed on this point. For example, some populations at low risk for STIs (e.g. Catholic priests) have shown a greater risk for prostate cancer compared to the general population, while others at high risk for STIs (e.g. men with HIV) have decreased rates of prostate cancer. Neither Wright et al. nor Spence et al. found any significant association between prostate cancer and a history of STIs, undermining their own working hypotheses.[136,137] The second assumption is that genitally intact men are at higher risk for STI. As seen above, the literature does not support this contention. Instead the literature indicates that circumcised men are at an overall greater risk of STIs.
If circumcision were actually to reduce the risk of prostate cancer, one would expect rates to have dropped in correlation to the rise in circumcision rates in the U.S. during the 20th century. In fact, the opposite has occurred. Likewise, one would expect to see an elevated incidence in non-circumcising Europe, compared to the circumcising U.S., and again, this has not been demonstrated. Finally, no association has been demonstrated between PSA levels (an indicator of likely prostate cancer) and circumcision status.