If you’re staring at a pathology report right now, you want the whole system in one place. This is the explainer that ran in Upgrade U, promoted to its own page.
A Gleason score is a grading system used to assess the aggressiveness of prostate cancer based on the appearance of cancer cells under a microscope. It comprises two numbers, each ranging from 1 to 5 (in practice, 3 to 5), and operates as follows:
The initial number represents the primary pattern & the second signifies the second most common pattern of cancer cells.
Both numbers indicate the extent to which the cancer tissue resembles normal prostate tissue:
1-2: Almost normal (rarely used in modern times)
3: Moderately abnormal
4: More abnormal, starting to lose structure
5: Very abnormal, aggressive, and lacking in structure
So:
3+3 = 6 → Grade Group 1 (low risk)
3+4 = 7 → Grade Group 2 (more concerning)
4+3 = 7 → Grade Group 3 (even more aggressive)
Anything 8–10 = Grade Groups 4 and 5 (high risk)
The short version: the lower the numbers, the lazier the cells look. The first number is the one to watch — it’s the pattern there’s most of. A 3+4 is not a 4+3: when the more aggressive 4 comes first, it’s a higher Grade Group, and the difference matters. It graded my labs in Labs — April 2025 and Upgrade U.