If cancer is present, the pathologist examines tissue samples from the prostate under a microscope to report the grade of the tumor. The grade of a tumour tells how much the tumour tissue differs from normal prostate tissue. It predicts how fast the tumour is likely to grow/progress. Tumours with higher grades tend to grow faster than those with lower grades. They are also more likely to spread. The Gleason score is a grading system for tumours. The pathologist gives each area of cancer a grade of 1 through 5. The Gleason score is retrieved by adding the two most common grades together or by adding the most common grade and the highest (most abnormal) grade. Gleason scores can range from 2 to 10. Tumours with a low Gleason score are less likely to show aggressive behaviour and therefore are less likely to spread outside of the prostate