Gleason Grade and Score
The Gleason score is named after Dr. Donald Gleason, the pathologist who first studied and devised a scoring system to describe the aggressiveness of prostate cancers. This system helps us to separate the less aggressive prostate cancers from those that are more aggressive. In more technical terms, it represents the "grade" of the tumor, which is a measure of the degree of differentiation of prostate cancer cells. Differentiation refers to how "normal" a cancer cell looks under a microscope when compared to a normal prostate cell. If the cancer is poorly differentiated or undifferentiated, then it looks very abnormal. If the cancer is well-differentiated, then it looks similar to normal cells.
As you might expect, the more aggressive cancers are poorly differentiated. These tumors have little or no regulation of their growth, allowing them to multiply in an uncontrolled manner (thus making it an aggressive cancer). Your Gleason score helps guide treatment options.
The Gleason score is actually a sum of two Gleason grades. The grade is a number from 1-5, with 1 being the most well-differentiated (looks more like normal cells) and 5 being the most poorly differentiated (looks more abnormal). The pathologist assigns a primary grade to the tumor cells that make up the majority of the tumor and a secondary grade to the cells making up a minority of the tumor. The Gleason score is then the sum of these two most dominant grades. Thus, the potential range of Gleason scores are from 2 (1+1) to 10 (5+5). The most prominent (primary) grade is either reported as the Gleason grade or is the first number in the score. For example:
- In a report of Gleason 7 (3+4), grade 3 is the most prominent.
- In a report of Gleason grade 4, score 7; grade 4 is the most prominent, with the total score being 7 (therefore grade 3 is the second most prominent score).
When a prostate is biopsied for diagnosis and then later removed with a radical prostatectomy, Gleason scores are the same between the biopsy and surgery specimens about 75% of the time. In about 20% of the cases, the surgery specimen actually ends up having a higher Gleason score (and thus a more aggressive cancer) than what was found on the initial biopsy. The reverse (lower Gleason score at surgery than at biopsy) happens less than 5% of the time. These discrepancies can be due to an incomplete biopsy or the expertise of the pathologist. Because the pathologist’s interpretation is subjective, it is important to have your tumor reviewed by an expert pathologist. Many experts recommend having a second pathologist review the specimen to be sure the Gleason grading is correct.
The Gleason score has been very clearly linked with expected trends in biochemical (PSA) relapse-free survival and overall survival. In other words, it is a very strong predictive and prognostic tool in the management of prostate cancer patients.
National Institute of Health: National Cancer Institute. (2013). Retrieved from https://www.cancer.gov/about-cancer/diagnosis-staging/prognosis/tumor-grade-fact-sheet
National Institute of Health: National Cancer Institute. (2019). Retrieved from https://www.cancer.gov/publications/dictionaries/cancer-terms/def/gleason-score