The grade is a term used to describe the microscopic appearance of prostate cancer and can help predict the potential aggressiveness of prostate cancer. Grade can be used as a measure to assess how likely prostate cancer is to grow and spread. The grading system most commonly used is called the Gleason score, which ranges on a scale from 2 to 10. In general terms, there are five different recognized patterns of prostate cancer (five different ways it can look under the microscope). The patterns are numbered Gleason grade 1 through 5. The pathologist can indicate which of these five patterns is present. In most cases, there is more than one pattern present, so the two most common patterns are identified. The Gleason score is a summary of the two most common patterns (for example, if there are some areas of Gleason grade 3 and other areas of Gleason grade 4, cancer may be assigned a Gleason score of 7).

From a practical point of view, clinical experience shows that most patients with prostate cancer have Gleason scores between 6 and 10. As the Gleason score increases, there is the potential for more aggressive disease. Higher Gleason scores (8 through 10) indicate more aggressive tumors which have the potential to have spread beyond the prostate.