When a pathologist looks at prostate cancer specimens under the microscope and gives them a Gleason grade, he or she in fact will always try to identify two architectural patterns and assign a Gleason grade to each one. There may be a primary or most common pattern and then a secondary or second most common pattern which the pathologist will seek to describe for each specimen; alternatively, there may often be only a single pure grade.
In developing his system, Dr Gleason discovered that by giving a combination of the grades of the two most common patterns he could see in any particular patient’s specimens, he was better able to predict the likelihood that that particular patient would do well or badly. Therefore, even though it may seem confusing, the Gleason score which a physician usually gives to a patient is actually a combination or sum of two numbers. These combined Gleason sums or scores may be determined as follows:
- The lowest possible Gleason score is 2 (1 + 1), where both the primary and secondary patterns have a Gleason grade of 1 and therefore when added together their combined sum is 2.
- Very typical Gleason scores might be 5 (2 + 3), where the primary pattern has a Gleason grade of 2 and the secondary pattern has a grade of 3, or 6 (3 + 3), a pure pattern.
- Another typical Gleason score might be 7 (4 + 3), where the primary pattern has a Gleason grade of 4 and the secondary pattern has a grade of 3.
- Finally, the highest possible Gleason score is 10 (5 + 5), when the primary and secondary patterns both have the most disordered Gleason grades of 5.
What does the Gleason score mean?
The grade of a prostate cancer specimen is very valuable to doctors in helping them to understand how a particular case of prostate cancer can be treated. In general, the time for which a patient is likely to survive following a diagnosis of prostate cancer is related to the Gleason score. The lower the Gleason score, the better the patient is likely to do.
