Clinical stage of cancer is determined only by physical examination of the prostate called a DRE (digital rectal examination).  The purpose of staging is to locate the cancer, but this is often inaccurate. In fact, compared to the PSA and Gleason score, staging of prostate cancer is the most inaccurate measure of the extent of your cancer. The biggest area of inaccuracy concerns stages T1 and T2 disease, the stages that most men have. In reality, onethird or more of men with stage T1 or T2 prostate cancer actually have stage T3 prostate cancer, cancer outside the prostate, due to microscopic capsule penetration of cancer cells, which cannot be detected before treatment.