Understanding Gleason Score
What Is the Gleason Score?
The Gleason score is a grading system used by pathologists to describe how aggressive prostate cancer cells look under a microscope. It was developed by Dr. Donald Gleason in the 1960s and remains one of the most important tools for predicting how a prostate cancer is likely to behave.
The score is based on the idea that more aggressive cancer cells look less like normal prostate cells. The more abnormal the cells appear, the higher the Gleason grade — and the more aggressive the cancer is considered to be.
How Is the Gleason Score Calculated?
A pathologist examines the biopsy tissue and assigns a grade from 1 to 5 to the two most common patterns of cancer cells seen in the sample:
- Primary grade: The most predominant pattern (the one that takes up the most space in the sample).
- Secondary grade: The second most common pattern.
These two grades are added together to produce the Gleason score. For example, if the primary grade is 3 and the secondary grade is 4, the Gleason score is 3+4=7.
In modern practice, grades 1 and 2 are rarely assigned on biopsy. Most Gleason scores you will see range from 6 to 10.
A Gleason score of 3+4=7 and a score of 4+3=7 are both '7,' but they are not the same. The first number is the dominant pattern. A 4+3=7 (more grade 4 present) is considered more aggressive than a 3+4=7, even though the total is identical.
What Do the Gleason Grades Mean?
Here is what each Gleason grade describes:
Grade 3
Grade 3: Cancer cells form small, well-defined glands that look somewhat like normal prostate tissue. This is the least aggressive pattern commonly seen on biopsy.
Grade 4
Grade 4: Cancer cells form poorly defined glands, fused glands, or cribriform (sieve-like) structures. Grade 4 is associated with more aggressive behavior.
Grade 5
Grade 5: Cancer cells show no gland formation at all — they grow in sheets, cords, or as single cells. This is the most aggressive pattern.
Common Gleason Scores at a Glance
| Gleason Score | Grade Group | Risk Level |
|---|---|---|
| 3+3=6 | Grade Group 1 | Low |
| 3+4=7 | Grade Group 2 | Favorable Intermediate |
| 4+3=7 | Grade Group 3 | Unfavorable Intermediate |
| 4+4=8 / 3+5=8 / 5+3=8 | Grade Group 4 | High |
| 9–10 | Grade Group 5 | Very High |
Note: Gleason scores of 6 or below are considered low-grade. Scores of 7 are intermediate. Scores of 8–10 are high-grade.
Because the scale runs from 6 to 10 in practice, some patients assume a 6 is average. In fact, Gleason 6 (Grade Group 1) is the lowest grade assigned and is associated with a very low risk of spread. This is an important distinction.
Limitations of the Gleason Score
The Gleason system has been refined over the decades, and the Grade Group system (introduced in 2014) was developed partly to address some of its limitations — including the confusion caused by a scale that effectively starts at 6, not 1.
See the Understanding Grade Groups guide for how the newer system maps to Gleason scores and what it means for your prognosis.
Many patients hear a Gleason score such as 7, 8, or 9 and immediately search the internet or assume they know what it means. Try not to judge your situation based on the Gleason score alone.
Your treatment recommendations are based on the whole picture—including your PSA level, MRI findings, biopsy results, Grade Group, stage, genomic testing (if performed), your age, overall health, and your personal goals.
Write down your questions before your appointment and ask your healthcare team to explain how your Gleason score fits into your overall diagnosis. That's far more important than the number by itself.