Where can I find the explanation of the Gleason score for rating prostate cancer?
Neha Vapiwala MD, Senior Editor for Oncolink, responds:
Thank you for your interest and question.
The Gleason score is named after Dr. Donald Gleason, the pathologist who first studied and devised a scoring system to describe the different categories of prostate cancer. 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 appears under microscopic evaluation by using a normal prostate cell as the standard. If the cancer is poorly differentiated or undifferentiated, then it looks very abnormal. If the cancer is well differentiated, then it looks more similar to normal cells. As you might expect, the more aggressive cancers are poorly differentiated, and these tumors have little or no regulation of their growth, allowing them to multiply in an uncontrolled manner (thus making it an aggressive cancer). The checks and balances that normal cells have to abide by are absent in these cancers.
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 and 5 being the most poorly differentiated pattern. The pathologist that examines the samples from a prostate biopsy will look at the two most poorly differentiated parts of the tumor and assign grades to these two areas. The Gleason score is then the sum of the two most dominant grades. Thus, the potential range of Gleason scores is from 2 (1+1) to 10 (5+5). Be aware that when a prostate is first biopsied for diagnosis and then subsequently removed with a radical prostatectomy, Gleason scores are the same between the biopsy and surgery specimens only 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 previously found on the initial biopsy. These patients may require additional treatment after surgery. The reverse (lower Gleason score at surgery than at biopsy) happens less than 5% of the time.
The Gleason score has been very clearly correlated 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. In essence, for the reasons described above, the higher the Gleason score, the poorer the patient's prognosis.