The journal Cancer has published a new study by Wright et al., entitled "Circumcision and the risk of prostate cancer".
It's an interesting read. It's a case-control study, with 1754 cases and 1645 age-matched controls, making it by far the largest study of prostate cancer and circumcision to date. 68.8% of cases were circumcised, compared with 71.5% of controls. The risk of prostate cancer was about 13% lower among circumcised men.
Complicating the issue somewhat was the timing of circumcision, as not all men had been circumcised at birth. The fact that some circumcised men had spent some of their lives with a foreskin obviously has an impact. Indeed, in the case of penile cancer the risk is actually greater in men circumcised after childhood, likely because such circumcisions tend to be associated with conditions such as phimosis and balanitis that themselves predispose towards penile cancer.
Wisely, the researchers performed sub-analyses taking into account the timing of circumcision. They found that men circumcised before first sexual intercourse had 15% lower risk of prostate cancer. Interestingly, there was a small difference in the type of cancer: the risk reduction was 12% for less aggressive forms and 18% for more aggressive types.
While not conclusive, this study is consistent with earlier studies that also found a protective effect against circumcision. My colleagues and I previously published cost analyses on circumcision vs prostate cancer.