If you have had prostate cancer, you probably know that the Gleason score is the most important factor in predicting your current state of prostate cancer and its probable outcome. The score is based on tumor grade -- an indication of the tumor's aggressiveness. Tumor grade reflects how far the cancer cells deviate from normal, healthy cells, which are highly organized, with well-defined structures.
Cancer cells display various degrees of disorganization and distortion and could be likened to a Jackson Pollock painting. Cancers whose cells appear closest to normal are considered grade 1 and generally are the least aggressive; those with highly irregular, disorganized features are classified as grade 5 and generally are the most aggressive.
The Gleason score is derived by determining the two most prevalent organizational patterns in the tumor, assigning each a grade, and then adding the two numbers together. For example, if the most common pattern is grade 3 and the next most common pattern is grade 4, the Gleason score would be 3 + 4 = 7. Most pathologists do not recommend assigning Gleason scores below 5 based on needle biopsies because when the prostate is removed and the entire gland is evaluated, lower Gleason scores are almost always upgraded.
Most urologists would classify Gleason scores of 5 and 6 as low-grade tumors, a Gleason score of 7 as intermediate, and Gleason scores of 8, 9, and 10 as high grade, with the least favorable outlook.
The Gleason score was originally devised by Donald F. Gleason, M.D., a pathologist who created the unique and now ubiquitous scoring system in the 1960s based on his observations of prostate tissue taken from biopsy samples of more than 300 patients. The prostate tissue, when riddled with microscopic tumors, had a certain pattern when viewed under a microscope, and Dr. Gleason took note of that, assigning numbers to the various architectural patterns. He finally arrived at five representative pictures that were characteristic of all the patients. When reviewing background data on the patients, a strong correlation was found between their "Gleason score" and the patients' death rates.
By the late 1980s, Dr. Gleason’s system was used in all medical publications on prostate cancer, and is still in use today throughout the world. Your PSA test result, along with your Gleason score, predicts the likely outcome of prostate cancer and it's the gold standard test that will be used to diagnose more than 186,000 men this year with the disease.
