A Gleason score is a number from 6 to 10 that describes how aggressive prostate cancer cells look under a microscope. It’s determined from a biopsy and is the single most important factor in predicting how a prostate cancer will behave. The score is written as two numbers added together, like 3+4=7, and the order of those numbers matters just as much as the total.
How the Score Is Calculated
When a pathologist examines prostate biopsy tissue, they look at how the cancer cells are arranged. Cells that still look somewhat organized and gland-like are lower grade. Cells that look chaotic, fused together, or barely resemble normal tissue are higher grade. Each pattern gets a number from 1 to 5, though in practice only patterns 3, 4, and 5 are used in modern grading.
The pathologist identifies the most common pattern in the sample (the primary grade) and the second most common pattern (the secondary grade), then adds them together. A biopsy where most of the cancer looks like pattern 3 with some pattern 4 would be scored 3+4=7. If only one pattern exists, it’s doubled, so a sample that’s entirely pattern 3 becomes 3+3=6.
If a small amount of a third, higher-grade pattern is present, it can replace the secondary grade in the equation. For example, a biopsy that’s mostly pattern 4 with some pattern 3 and a small area of pattern 5 would be reported as 4+5=9 rather than 4+3=7. This ensures the most dangerous-looking cells influence the final score.
Why the Order of Numbers Matters
A Gleason score of 3+4=7 and 4+3=7 add up to the same total, but they carry very different risks. The first number represents the dominant pattern in the tumor, so 4+3 means more of the cancer is made up of the more aggressive pattern 4 cells.
The survival data makes this gap concrete. In a population-based study, 10-year prostate cancer survival was 92.1% for men with 3+4 tumors and 76.5% for men with 4+3 tumors. Among men who received surgery or radiation, those with 4+3 cancers had roughly twice the risk of the cancer recurring and more than three times the risk of dying from it compared to men with 3+4 cancers. This is why modern pathology reports always write out the full equation rather than just the total.
Grade Groups: The Updated System
In 2014, the International Society of Urological Pathology introduced a simpler five-tier system called Grade Groups, which now appears alongside the Gleason score on most pathology reports. The mapping works like this:
- 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 (4+4, 3+5, or 5+3)
- Grade Group 5: Gleason 9 or 10 (4+5, 5+4, or 5+5)
One advantage of this system is psychological. A Gleason 6 sounds alarming when you know the scale goes to 10, but calling it Grade Group 1 makes it clearer that this is the lowest category of prostate cancer, with a distinctly different outlook from higher scores. The system also formally separates 3+4 and 4+3 into different groups, reinforcing that they are not equivalent.
What Each Score Range Means
Gleason 6 (Grade Group 1)
This is the lowest score assigned to prostate cancer. The cells still form recognizable gland-like structures and tend to grow slowly. Ten-year prostate cancer survival is about 98.4%. Many men with a Gleason 6 cancer are candidates for active surveillance, meaning the cancer is monitored with regular check-ups and repeat biopsies rather than treated immediately. Active surveillance is typically appropriate when the cancer is small, confined to one area of the prostate, and not causing symptoms.
Gleason 7 (Grade Groups 2 and 3)
This is the most common score range and the one where the distinction between 3+4 and 4+3 is critical. A 3+4 cancer is considered intermediate risk, with strong long-term survival and several treatment options. A 4+3 cancer is more aggressive and typically prompts more active treatment decisions. Five-year survival is about 98.9% for 3+4 and 88.6% for 4+3, but the gap widens over longer follow-up periods.
Gleason 8 to 10 (Grade Groups 4 and 5)
Roughly 15% of men diagnosed with prostate cancer in the U.S. have high-risk disease, and a Gleason score of 8 to 10 is one of the defining features. These cancers contain large amounts of pattern 4 or pattern 5 cells, which grow in disorganized sheets or lose any gland-like structure entirely. Gleason 9 and 10 cancers are particularly aggressive, with more frequent spread to distant sites and earlier recurrences after treatment. These cancers follow a shorter timeline than lower-grade prostate cancers, which can take years or even decades to progress.
The Tertiary Pattern
Sometimes a biopsy or surgical specimen contains a small area of very aggressive pattern 5 cells alongside a lower overall score. This is called a tertiary pattern, and it acts as a warning flag. A cancer scored 3+4 with a tertiary pattern 5 is more likely to have grown beyond the prostate capsule and to have a larger tumor size than a straightforward 3+4 cancer. Similarly, 4+3 with tertiary pattern 5 is associated with a significantly shorter time to recurrence compared to 4+3 alone. In multivariate analysis, the presence of tertiary pattern 5 was an independent risk factor for recurrence, nearly doubling the hazard. Your pathology report may note this tertiary pattern separately.
Biopsy Scores Can Change After Surgery
A Gleason score from a needle biopsy is based on small tissue samples, so it doesn’t always match the score from the full prostate after surgical removal. In one study of 174 men, about half had a score change between biopsy and surgery. The vast majority of changes were upgrades, meaning the final score was higher than the biopsy suggested. Only a small number were downgraded. This happens because a needle biopsy samples only a fraction of the prostate and can miss higher-grade areas.
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. No single number tells the whole story, but the Gleason score remains the strongest individual predictor of how a prostate cancer will behave over time.
Other Terms on Your Pathology Report
Your biopsy results will include more than just a Gleason score. A few terms you might see: perineural invasion means cancer cells were found growing around a nerve fiber inside the prostate. Intraductal carcinoma, if present alongside regular prostate cancer, can indicate a more aggressive form. You may also see notes about conditions that are not cancer, such as chronic inflammation, atrophy, or high-grade prostatic intraepithelial neoplasia (PIN), which is an abnormal cell pattern that is not cancer itself but is sometimes found near cancerous areas. These additional findings help your care team build a complete picture of your cancer’s characteristics.