Can the Gleason Score on my biopsy really tell what the cancer grade is in the entire prostate?

Prostate biopsies are tissue samples from different areas of the prostate.  The Gleason Score on a biopsy usually reflects the cancer's true grade.  However, it is possible that the Gleason Score from your biopsy is lower or higher than the true grade.  To reduce the risk of over-or-under scoring, multiple biopsies are usually taken from different areas within the prostate.