A new analysis has found evidence that circumcision may reduce the risk for prostate cancer.

Researchers studied 1,754 men with prostate cancer and 1,654 controls in King County, Wash. They asked the men if they were circumcised and if they had ever had a sexually transmitted infection. The investigators also gathered information on prostate cancer from a tumor registry.

The study, published Monday in the journal Cancer, controlled for age, race, family history of prostate cancer and other factors. The scientists found that circumcision before first sexual intercourse was associated with a 15 percent lower risk for prostate cancer.

There is evidence for the role of germs in the development of several cancers — cervical, liver and stomach cancer among them. And there is good evidence that circumcision can reduce rates of sexually transmitted diseases. Sexually transmitted germs have been found in the prostate, including chlamydia, H.I.V., and HPV.

Although the exact mechanism remains unknown, the authors suggest that circumcision eliminates the possibility of germs flourishing in the moist environment under the foreskin, and reduces the chance for infection.

“These are observational data that don’t prove causality,” said the lead author, Dr. Jonathan L. Wright, an assistant professor of medicine at the University of Washington. “But there is some role for inflammation in several cancers, and this helps bolster that argument.”