When diagnosing prostate cancer, a Gleason score is used to determine how aggressive the cancer is. Before understanding what the Gleason score means, one should know how a Urologist comes up with a Gleason score in the first place. To identify the Gleason score, a Urologist will do a prostate biopsy which involves collecting prostate tissue samples. These prostate tissue samples are then sent to a lab to be analyzed by a pathologist. The pathologist will determine the Gleason score which is made up of two numbers: a primary grade and a secondary grade.