What Is the Gleason Score? How Are Gleason Grades Calculated in Prostate Cancer?

The Gleason score evaluates prostate cancer cells’ degree of differentiation from normal cells and provides an indication of how quickly cancer cells grow and spread. The Gleason score ranges from 2-10; a higher score indicates more aggressive cancer and faster progression.

Under a microscope, the pathologist examines a tissue sample obtained through a prostate biopsy for Gleason patterns. These patterns are expressed as numbers from 1 to 5. Under the microscope, pattern 1 cancerous prostate cells resemble normal prostate glands, whereas in pattern 5 the normal glandular appearance is very rare or entirely absent. This corresponds to anaplastic carcinoma.

The pathologist then identifies the predominant patterns in the tumor sample. The dominant pattern is called the primary pattern and must account for more than 50% of all observed patterns. Secondary patterns, accounting for more than 5% but less than 50%, and tertiary patterns are then determined according to their frequency.

Finally, the pathologist calculates the final Gleason score by adding the primary and secondary pattern numbers. If only 2 patterns are present, the primary and secondary numbers are added. If 3 patterns are present, the primary pattern and the high-grade pattern are added. For example, if the primary pattern score is 2, the secondary score is 3, but some cells are grade 4, the Gleason score is 2+4=6.