How the Gleason Score Is Key to Understanding Your Prostate Cancer Prognosis
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If you’ve recently been diagnosed with prostate cancer, or if you’ve had a prostate biopsy to test for prostate cancer, you might have seen the term “Gleason score” or “Gleason grade” on the pathology report. This number gives your doctor information about how your prostate cancer might behave in the coming days or years.
What Is a Gleason Score?
The Gleason score is a grading system for prostate cancer that rates how aggressive the disease is, which helps doctors determine your prognosis and treatment. Named after pathologist Donald Gleason, who developed the grading system in the 1960s, the Gleason score is a crucial component in assessing prostate cancer.
The Gleason score provides a “grade” for the cancer, which is different from the cancer’s stage. A cancer’s stage refers to where the cancer is present in the body, the size of the tumor, and how far it has spread. The grade refers to the microscopic appearance of cancer cells.
When a person has prostate cancer, the prostate cells are mutating or changing, becoming abnormal. Early in the development of the disease, cancer cells may look like healthy cells. The closer the cancer cells look like normal cells, the lower the grade. But they will slowly change over time and become more abnormal in appearance, corresponding to a higher grade.
Cells in one part of a tumor may look different from cells in other parts, meaning one part of a tumor may have a higher grade than another. The Gleason score provides an understanding of these variations by incorporating grades from two areas that make up most of the cancer.
How Is the Gleason Score Calculated?
To calculate your Gleason score, a pathologist will use a microscope to examine the cells from the tissue sample collected from your biopsy and look at the major patterns of cancer cells in your prostate tissue.
Each pattern is assigned a grade on a scale from 1 to 5, with 1 meaning your cancer tissue looks a lot like normal prostate tissue and 5 meaning the cancer cells look very abnormal. Patterns with grades 2 through 4 have features between these extremes, though almost all prostate cancer cells are given a score of 3 or higher, according to the American Cancer Society.
Pathologists then add the grades of the two most prevalent cancer cell patterns observed to create the Gleason score. If the primary pattern, or the most common pattern, is grade 3 and the secondary pattern is grade 4, the Gleason score is 3+4=7. If the tumor is the same grade everywhere, that grade is added to itself for the total score (for example, 4+4=8).
What Does the Gleason Score Mean?
The Gleason score provides insight into the aggressiveness of the prostate cancer, or how quickly it grows or spreads. Lower scores suggest less aggressive tumors, while higher scores indicate more aggressive tumors.
Specifically, the Gleason score divides prostate cancer into three groups:
Gleason 6: The cancer is low-grade, sometimes called “well differentiated.”
Gleason 7: The cancer is intermediate-grade or “moderately differentiated.”
Gleason 8–10: The cancer is high-grade or “poorly differentiated.”
Gleason scores below 6 are rarely used and indicate very slow-growing cancers that are less likely to be considered significant.
Although this ultimate score, also known as the Gleason sum, is an important figure for understanding a prostate cancer prognosis, it doesn’t tell the whole story. Pathologists also consider the individual grades that make up the sum when determining the overall aggressiveness of the disease. For example, a Gleason score of 4+3=7 (where the primary pattern is grade 4) indicates a higher-risk cancer than 3+4=7 (where the primary pattern is grade 3) because more of the cancer cells are grade 4 than grade 3.
Though uncommon, it’s also possible that the biopsy missed a higher grade or more aggressive cancerous area somewhere else in the prostate. Pathologists may also disagree on the Gleason score, which can happen up to 30 percent of the time, so seeking a second opinion might be something to consider.
Gleason Score vs. Grade Group
The Gleason score can be confusing to understand. A score of 6, for example, may sound like the cancer is in the middle range rather than the lowest grade seen in practice. Having two different meanings for a score of 7 can also cause confusion.
For this reason, in 2014, the International Society of Urological Pathology consensus conference recommended changing the Gleason scoring system by categorizing the scores into five grade groups:
Grade Group 1: Gleason score 6 or less
Grade Group 2: Gleason score 7 (3+4)
Grade Group 3: Gleason score 7 (4+3)
Grade Group 4: Gleason score 8
Grade Group 5: Gleason score 9–10
What Does the Gleason Score and Grade Group Tell Me About Risk?
Both the Gleason score and grade group are useful for assessing the risk associated with prostate cancer, but the grade groups may provide a more intuitive way to understand the severity of the disease. The grade group plays a pivotal role in guiding treatment decisions, monitoring, and follow-up tailored to individual patients.
Grade group 1 tumors are low-risk and have a better prognosis, while higher-grade groups indicate more aggressive cancer behavior, faster progression, more potential to spread to other organs (metastasize), and greater risk of recurrence. For individuals with low-grade tumors (grade group 1), active surveillance may be a viable option, allowing patients to avoid unnecessary treatments like surgery and radiation that may cause unwanted side effects. These low-grade tumors may also warrant less frequent follow-up.
On the other hand, higher grade groups may prompt more assertive treatments — such as surgery, radiation, or hormonal therapy — and more vigilant monitoring to detect signs of progression or recurrence early on.
