The Gleason score is a grading system that describes how aggressive prostate cancer cells look under a microscope, scored on a scale from 6 to 10. A pathologist examines tissue from a prostate biopsy, identifies two dominant growth patterns, and adds them together. The resulting number helps predict how quickly the cancer is likely to grow and spread, making it one of the most important factors in deciding treatment.
How the Score Is Calculated
When a pathologist examines a biopsy sample, they look at the cancer cells and identify how closely they resemble normal, healthy prostate tissue. Prostate cancer typically shows two main growth patterns in the same sample. Each pattern gets a grade from 1 to 5, though in practice grades 1 and 2 are almost never assigned in modern pathology.
The primary pattern is the one that makes up more than 50% of the cancer in the sample. The secondary pattern is the second most common. The pathologist adds these two numbers together to produce the Gleason score. So a biopsy where the most common pattern is grade 3 and the second most common is grade 4 would be reported as 3+4=7.
This means the lowest score you’ll realistically see on a modern pathology report is 6 (3+3), and the highest is 10 (5+5). The individual pattern numbers matter just as much as the total, which is why your report will always show the breakdown rather than just a single number.
What the Patterns Actually Describe
Each pattern grade reflects how disorganized the cancer cells have become. Grade 3 glands are well-formed and individually separated, with clear boundaries between them. They still look somewhat like normal prostate tissue, just arranged abnormally. Grade 4 glands start fusing together, lose their distinct shape, and form complex, poorly defined structures. Grade 5 loses gland formation entirely, with cancer cells spreading as individual units rather than forming any recognizable glandular structure.
The higher the pattern number, the less the cells resemble normal tissue, and the more likely they are to grow and spread aggressively.
Why 3+4 and 4+3 Are Not the Same
Both 3+4 and 4+3 add up to 7, but they carry very different prognoses. In a 3+4 tumor, the majority of the cancer is the less aggressive pattern 3, with some pattern 4 mixed in. In a 4+3 tumor, the more aggressive pattern 4 dominates.
A study published in the Journal of Clinical Oncology found that men with 4+3 cancers on surgical specimens were 3.1 times more likely to die of prostate cancer than men with 3+4 cancers. The crude cancer mortality rates tell the story clearly: 11.0 deaths per 1,000 person-years for 3+4 on biopsy, compared to 18.7 for 4+3. That gap widened further at higher scores, with Gleason 8 at 40.6 and Gleason 9-10 at 98.8 per 1,000 person-years. The dominant pattern is the more important number.
The Grade Group System
Because the old Gleason scale created confusion (patients hearing “6 out of 10” often assumed they were in the middle of the severity range, when 6 is actually the lowest assigned score), the International Society of Urological Pathology introduced a simpler five-tier system called Grade Groups. Most pathology reports now include both.
- Grade Group 1: Gleason 3+3=6
- Grade Group 2: Gleason 3+4=7
- Grade Group 3: Gleason 4+3=7
- Grade Group 4: Gleason 8 (various combinations of patterns 3, 4, and 5)
- Grade Group 5: Gleason 9-10
This system makes the separation between 3+4 and 4+3 explicit and gives patients a more intuitive sense of where they fall. Grade Group 1 is the least aggressive, and Grade Group 5 is the most.
What a Tertiary Pattern Means
Sometimes a pathologist identifies a third pattern occupying a small amount of the cancer, typically less than 5%. This is called a tertiary pattern. It matters most when a higher-grade pattern shows up as the third component in an otherwise lower-grade cancer.
For example, a Gleason 3+3=6 cancer that also contains a small amount of pattern 4 (called “6 with tertiary pattern 4”) falls into a gray zone. Research shows these cancers carry risk that sits between a standard Gleason 6 and a Gleason 3+4=7. Five-year progression-free survival was 93% for standard Gleason 6, 85% for Gleason 6 with tertiary pattern 4, and 76% for Gleason 3+4=7. On biopsies, current guidelines recommend folding the tertiary pattern into the score itself, so a biopsy with even a small amount of pattern 5 alongside pattern 4 would be reported as Gleason 4+5=9.
Biopsy Scores Can Change After Surgery
A biopsy samples only small portions of the prostate, so it doesn’t always capture the full picture. When the entire prostate is removed and examined, the Gleason score matches the biopsy result only about 50% of the time. In roughly 24% of cases the score goes up, and in about 26% it goes down. This is one reason doctors consider the Gleason score alongside other factors like PSA levels, imaging results, and the number of biopsy cores that contain cancer.
How the Score Shapes Treatment Decisions
Grade Group 1 (Gleason 6) cancers are the least aggressive, and active surveillance is the recommended approach for most men in this category. Active surveillance means regular monitoring with PSA tests, repeat biopsies, and imaging rather than immediate treatment. No lethal prostate cancer events occurred among men with Gleason 6 in large long-term studies, which is why many experts consider these cancers very low risk.
Grade Group 2 (Gleason 3+4=7) sits in a more nuanced space. Guidelines from major organizations now include select Grade Group 2 patients as candidates for active surveillance, but only under specific conditions: low PSA (under 10), low volume of disease on biopsy, a small percentage of pattern 4, and early clinical stage. If the pattern 4 component shows a specific growth arrangement called cribriform pattern, European guidelines recommend against surveillance because this feature is linked to worse outcomes.
Grade Group 3 and above (Gleason 4+3=7 or higher) generally calls for active treatment. The specific approach depends on many factors beyond the Gleason score alone, but higher grade groups correlate with greater risk of the cancer spreading beyond the prostate. Men with high-volume Grade Group 2 or any Grade Group 3 cancer face considerably higher risks of poor outcomes if managed with surveillance alone.