Named after the American pathologist Donald Gleason (b. 1920), the Gleason score is a system of determining the severity of cancer of the prostate gland.
The score ranges in value from 2 to 10, and is determined by adding two numbers, each of which relates to the appearance of the two main types of cancer cells seen through a microscope when a biopsy of a prostate cancer is examined.
If the cancer cells closely resemble the normal prostate tissue, a score of 1 is given, and the cancer is not likely to spread quickly. If the cells are very irregular and abnormal the cancer is likely to be more aggressive and a score of 5 is given. The intermediate numbers are used for intermediate stages of cancer cell abnormality. If one type of cancer cell is quite abnormal (score 4) and the other relatively normal (score 2) the total Gleason score will be 6.