To date, prostate-specific antigen (PSA) has proven to be the most useful tumor marker for prostate cancer (1 –3 ). However, the PSA test does not discriminate well between men with benign disease and early prostate cancer, and it does not discriminate between aggressive and slow-growing cancers (4 ,5 ). Although a useful additional discriminator (5 ), the advent of free/total PSA assays has not significantly improved this outcome. Thus, an inability to make an early diagnosis has led to the increased burden of metastatic disease, and many patients are overtreated because clinically aggressive disease cannot be distinguished from clinically insignificant disease.