Doctors have long debated how and whether to treat early cases.
But the benefit may depend on how a man is diagnosed.
About 95 percent of the cancers in the study were found because they were causing symptoms. However, in the United States, most cancers were found by blood tests, long before symptoms appeared.
Even though most of these cancers will not prove to be life-threatening, there is no way to determine which ones will, so many men end up getting treatment they may not need.
The Associated Press contributed to this story.