Pathology dictionary -
The Gleason grade is an internationally recognized system used to describe the microscopic changes seen in prostate cancer. The Gleason grade can only be determined after a sample of the tumour has been examined under the microscope.
The Gleason grade is determined by examining tumour cells and determining how different they look from normal prostate glands. After examining the tumour under the microscope, your pathologist will give the tumour a number between 1 and 5. Tumours that look similar to normal glands are given a lower number. These tumours tend to be slow growing and less aggressive. Tumours that do not look like normal glands are given a higher number and tend to be more aggressive. These tumours can grow quickly and spread.
Why is this important? The Gleason score is important because it can be used to predict the behavior of the tumour. It is determined by adding up the two most prevalent Gleason grade numbers.
Examples of different Gleason grade prostate cancers
For example, if your tumour is composed of 70% Gleason grade 3 and 30% Gleason grade 4, then your Gleason score would be 3+4=7. If only one Gleason grade is present then the primary and secondary patterns are given the same grade. For example, if your tumour is composed 100% of Gleason grade 3, then your Gleason score is 3+3=6.
It is very important to know that Gleason grade 1 and 2 tumours are practically never diagnosed. These grades are significant for historical purposed only and should not be diagnosed in modern practice. Consequently, Gleason grades actually range from 3-5 (instead of 1-5) and Gleason scores are from 6 to 10 (instead of 2-10).
A Gleason score 3+3=6 tumour is considered low grade. The malignant glands resemble normal prostate glands. These tumours are slow growing and incapable of spreading. If found on a biopsy, Gleason score 3+3=6 tumours may be managed by Active Surveillance (please see "Active Surveillance" below).
In contrast, Gleason score tumours equal to or greater than 8 (for example 4+4=8, 4+5=9, 5+4=9, and 5+5=10) are considered high grade. That is they look very little like normal prostate glands. These tumours tend to behave in an aggressive fashion.
In between the Gleason score 6 and equal to or greater than 8, are Gleason score 7 tumours (for example 3+4=7 and 4+3=7). These tumours bear only a moderate resemblance to normal glands. The prognosis for these tumours lies somewhere between the low grade Gleason score 6s and the high grade Gleason score equal to or greater than 8s.