The Gleason Score is a grading method for prostate cancer – this signifies how aggressive the cancer is.  It uses a number that ranges from 2 to 10 to grade the aggressiveness of prostate cancer, with a higher number indicating an increased likelihood that the cancer will spread. The score is made by combining two numbers, the primary Gleason grade and secondary Gleason grade, each scored from 1 to 5. 

The primary Gleason grade is determined by a pathologist based on the most common tumor pattern and its level of differentiation (how different the healthy and cancerous cells are from each other). 

The secondary Gleason grade is done the same way as the primary except it is based on the second most common tumour pattern.