When deciding upon a management strategy for prostate cancer, it is important to understand that prostate cancer is a highly variable cancer with a wide range of risk. The risk and expected behavior from a given prostate cancer is identified by the pathologist and described in the form of a Gleason sum or score. This is a number between 2 and 10 assigned to the prostate cancer by the pathologist based upon the appearance of the prostate cancer cells under the microscope. Dr. Gleason, for whom this score is named was a pathologist specializing in prostate cancer. He was also an artist and had an eye for patterns. He observed in the course of his work, that prostate cancer cells formed into one of five different patterns. He described and made drawings of these patterns proposing that the cell type that forms one pattern may behave differently than the cell type that forms another pattern. By recognizing the patterns present in a given prostate cancer, we might be able to predict that cancers’ behavior. He described this in 1966. It was adopted by pathologists and still used today.
To derive the Gleason score, a pathologist examining a prostate specimen will look for the dominant pattern and assign the appropriate number to that pattern. The pathologist will then look for a secondary pattern and number that as well. These numbers are added together to produce a sum or score between 2 and 10. This score and the PSA are used to stratify men into one of four categories of risk. Each risk category is then managed a little differently. Depending upon the risk category, derived from the Gleason score, a man may be observed with active surveillance, require definitive therapy, or if in a high risk category, require multimodal therapy.