The PSA (prostate-specific antigem) test has become a routine tool for detecting prostate tumors. This is predicated on the fact that PSA levels rise when prostate cancer is present, although levels can go up for other reasons as well. A level greater than 10 is high; values between 4 and 10 are borderline. About one-third of men with a PSA level between 4 and 10 will prove to have cancer. Because PSA levels also rise with age, a higher reading in a younger man might be more suspicious than the same reading in an older man. The key to curing prostate cancer is early detection.