A system of grading prostate cancer tissue based on how it looks under a microscope. Gleason scores range from 2 to 10 and indicate how likely it is that a tumor will spread. A low Gleason score means the cancer tissue is similar to normal prostate tissue and the tumor is less likely to spread; a high Gleason score means the cancer tissue is very different from normal and the tumor is more likely to spread.
Last updated: 2016-01-06
Source: The National Cancer Institute's Dictionary of Cancer Terms (http://www.cancer.gov/dictionary)