MONDAY, March 12 (HealthDay News) -- Men who have prostate cancer are less likely to be circumcised, according to new research.

The researchers suggest a possible reason is that circumcision reduces the risk of sexually transmitted diseases that may contribute to prostate tumors.

The study doesn't confirm that circumcision directly lowers the risk of prostate cancer, and the study lead author cautioned that the findings shouldn't play a role in the decisions of parents about the sometimes-controversial procedure.

Still, the results fit in with existing knowledge about how cancer develops, said study author Dr. Jonathan Wright, a urologic oncologist at the Fred Hutchinson Cancer Research Center at the University of Washington in Seattle.

"It helps us to understand how cancers develop and ultimately learn how to combat the disease," he said.

Circumcision is the removal of the foreskin that covers the penis tip, and it is usually done shortly after birth. Opponents say the procedure is unnecessary, painful and a disfigurement that robs men of sexual sensation. But research in recent years has suggested that circumcision reduces the risk of sexually transmitted diseases like HIV, the virus that causes AIDS. Scientists think circumcision does that by eliminating the ability of germs to lurk under the foreskin.

Previous research by the study authors found no link between circumcision and lower risk of prostate cancer. But the new study is larger, Wright explained.

The researchers examined medical records and surveys of 1,754 men who were diagnosed with prostate cancer in the Seattle area and 1,645 similar men who were healthy.

Of those with prostate cancer, about 65 percent had been circumcised before the first time they had intercourse, compared with 69 percent of the healthy men.

Those with prostate cancer were still less likely to have been circumcised after the researchers adjusted their statistics so they wouldn't be thrown off by factors like high or low numbers of men of certain incomes, education levels or race.

However, the study doesn't prove that circumcision has anything to do with prostate cancer. Some other factor could explain this difference between the men with prostate cancer and the healthy ones, or it could be a statistical fluke.

But it makes sense that germs from sexually transmitted diseases would find it easier to get into the body, and then into the prostate, in the uncircumcised men, Wright said. It's possible that "they set up shop in the prostate and turn on inflammation, and then the inflammation leads to cancer development," he said.

Research has linked infections to some kinds of cancer, he explained.

Brian Morris, a professor of molecular medical sciences at Australia's University of Sydney who studies circumcision, praised the study's design and said it "provides even more reason for parents to opt for this 'surgical vaccine.'" Circumcision protects baby boys from urinary infections that can damage their kidneys as well as other diseases over their lifetimes, he said.

Natasha Larke, a lecturer in epidemiology and medical statistics at the London School of Hygiene & Tropical Medicine who has studied circumcision, said the study was well done, although there were limitations. For one, the study didn't include all prostate cancer patients in the Seattle region, she said. And even if a possible effect of circumcision is confirmed, it appears to be "modest," Larke added.

The study was published March 12 in the journal Cancer.

While the study found an association between circumcision and lower risk of prostate cancer, it did not prove a cause-and-effect relationship.

More information:

For more about prostate cancer, try the U.S. National Library of Medicine.