A Gleason score is determined by a pathologist who examines prostate tissue under a microscope, identifies the two most common patterns of cancer cell growth, assigns each pattern a grade from 1 to 5, and adds them together. The result is a score ranging from 2 to 10, though in modern practice scores below 6 are rarely assigned. The number you see on your pathology report, something like “3+4=7,” tells you both which patterns were found and how much of each was present.
What the Pathologist Looks For
After a prostate biopsy or surgery, thin slices of tissue are placed on glass slides and stained so the cellular structures become visible. The pathologist is looking at one thing above all: how much the cancer cells still resemble normal prostate glands. Normal prostate tissue forms small, round, well-organized glands. Cancer disrupts that architecture, and the worse the disruption, the higher the grade.
Each area of cancer in the sample gets a grade from 1 to 5. In practice, grades 1 and 2 are almost never used today because those patterns are nearly indistinguishable from normal tissue and rarely behave aggressively. The grades that matter are 3, 4, and 5:
- Pattern 3: The cancer still forms individual, distinct glands. They may vary in size and shape, but each gland is separate and recognizable. This is the most favorable pattern found in modern diagnoses.
- Pattern 4: The glands start merging together, forming fused clusters, poorly shaped structures, or a sieve-like (cribriform) arrangement where cells form sheets with small holes punched through them. The organized gland structure is breaking down.
- Pattern 5: Gland formation is essentially gone. The cancer grows as solid sheets or individual scattered cells, sometimes with areas of dead tissue. This is the most aggressive pattern.
How the Two Numbers Are Added
Prostate cancer is rarely uniform. Different areas within the same biopsy can look very different under the microscope. The pathologist identifies the pattern that makes up the largest portion of the cancer (the primary pattern) and the pattern that makes up the second largest portion (the secondary pattern), then adds them together.
The first number in the score is always the primary (most common) pattern, and the second is the secondary pattern. So a score of 3+4=7 means most of the cancer is pattern 3, with a smaller amount of pattern 4. A score of 4+3=7 is the same total but a different cancer: mostly pattern 4 with some pattern 3. That order matters because the dominant pattern drives behavior. A 4+3 cancer is more aggressive than a 3+4, even though both add up to 7.
Occasionally the pathologist sees a third, minor pattern that makes up less than 5% of the specimen. In a surgical sample, this gets noted as a “tertiary pattern” in the report. A tertiary pattern 5, even in small amounts, can signal that a small pocket of highly aggressive cancer is present.
Biopsy vs. Surgical Specimens
Most Gleason scores come from a needle biopsy, where a urologist takes 10 to 12 thin cores of tissue from different areas of the prostate. The pathologist grades each core individually, and the highest score among all the cores typically drives treatment decisions.
The limitation is that a biopsy only samples a small fraction of the prostate. When the entire gland is later removed during surgery and examined, the score changes in roughly 35% of cases, almost always going up. This is called Gleason upgrading, and it happens because the biopsy needle may have missed the most aggressive area of the tumor. Image-guided biopsy techniques, including MRI-targeted approaches, have improved accuracy but haven’t eliminated sampling error entirely.
This upgrading risk is particularly important for men considering active surveillance, where the cancer is monitored rather than immediately treated. A biopsy showing only low-grade cancer might lead to a surveillance recommendation, but if the true grade is higher, that approach could delay needed treatment.
Grade Groups: The Newer System
In 2014, the International Society of Urological Pathology introduced a simplified system called Grade Groups, numbered 1 through 5. You’ll often see both systems on a pathology report. The mapping works like this:
- Grade Group 1 (Gleason 6 or lower): Only well-formed, separate glands. The most favorable category.
- Grade Group 2 (Gleason 3+4=7): Mostly well-formed glands with a smaller component of fused or poorly formed glands.
- Grade Group 3 (Gleason 4+3=7): Mostly poorly formed or fused glands with a smaller component of well-formed glands.
- Grade Group 4 (Gleason 8): Only poorly formed glands, or a mix of patterns that averages to 8.
- Grade Group 5 (Gleason 9 or 10): Cancer that largely or entirely lacks gland formation, sometimes with areas of dead tissue.
The Grade Group system was created partly to solve a communication problem. When patients heard “Gleason 6 on a scale of 2 to 10,” many assumed they were in the middle of the range and panicked. In reality, 6 is the lowest score given in modern practice and carries an excellent prognosis. Calling it “Grade Group 1 out of 5” makes that clearer.
Why the Score Matters for Treatment
The Gleason score is one of three pillars doctors use to assess prostate cancer, alongside the PSA blood test level and the clinical stage (how far the cancer has spread on imaging or physical exam). Together, these determine whether you’re looking at active surveillance, radiation, surgery, or other approaches.
Grade Group 1 cancers grow slowly and rarely spread. Many men with this result are offered active surveillance with regular monitoring rather than immediate treatment. Grade Group 2 cancers are still relatively favorable but carry more risk, and treatment decisions become more individualized. By Grade Group 4 and 5, the cancer is aggressive. Research on men with Gleason 9 and 10 cancers shows 10-year cancer-specific survival rates around 70 to 73%, meaning these scores prompt urgent and typically multimodal treatment.
Even within the same score, the specific patterns matter. A Gleason 8 made up of 4+4 may behave differently than one made up of 3+5. And the presence of certain structures, particularly the cribriform pattern within Gleason 4, is increasingly recognized as a marker of more aggressive behavior. Some pathology reports now specifically note whether cribriform growth is present, because it can influence how aggressively your doctors recommend treating even an intermediate-grade cancer.
What Your Report Will Look Like
A typical pathology report lists results for each biopsy core separately. You might see something like “Core 3: Gleason 3+4=7, Grade Group 2, 40% of core involved” alongside “Core 7: Gleason 4+4=8, Grade Group 4, 15% of core involved.” The percentage tells you how much of that particular core contained cancer. The highest Gleason score from any core, the number of cores positive for cancer, and the percentage of each core involved all factor into treatment planning.
If you’ve had surgery, the report covers the entire gland and gives a single overall Gleason score plus information about whether the cancer reached the edges of the removed tissue (margins), whether it extended outside the prostate capsule, and whether nearby lymph nodes were involved. This surgical pathology is considered the most accurate assessment because the pathologist can examine every part of the gland rather than relying on small needle samples.