Doctors use the Gleason score to describe how dangerous a cancerous prostate tumor is in terms of how likely it is to spread. Gleason scores range from one to 10, where a one is a tumor that is less likely to spread, and a 10 is a tumor more likely to spread, making it more dangerous. Scores of six and under are all classified as low-grade cancers, seven as midgrade, and eight or above as high grade, according to Cancer.net.
Doctors determine how easily a tumor may spread by how much its cells resemble healthy tissue cells. Cells that are similar to healthy tissue are less likely to spread, whereas cells that differ greatly are more likely. Doctors decide a tumor's similarity to regular tissue through a biopsy, where they remove pieces of the tumor for inspection. A pathologist looks at the tumor under a microscope, and gives individual groups of cells their own Gleason scores. He or she then adds the two most commonly occurring scores, the sum of which is the patient's overall Gleason score, explains Cancer Research UK.
The Gleason score is used alongside two other major prognostic factors. The first factor is a tumor's stage, which describes a tumor's location, if it has spread, and if it is affecting other bodily organs. The second factor is a PSA test that measures certain antigen levels in a patient's blood. These three factors, when combined, allow doctors to give a prognosis and design a treatment plan for prostate cancer, according to Cancer.net.