The Gleason score and what it means

The Combined Gleason Score or Gleason Sum

When a pathologist looks at prostate cancer specimens under the microscope and gives them a Gleason grade, he or she in fact will always try to identify two architectural patterns and assign a Gleason grade to each one. There may be a primary or most common pattern and then a secondary or second most common pattern which the pathologist will seek to describe for each specimen; alternatively, there may often be only a single pure grade.

In developing his system, Dr Gleason discovered that by giving a combination of the grades of the two most common patterns he could see in any particular patient’s specimens, he was better able to predict the likelihood that that particular patient would do well or badly. Therefore, even though it may seem confusing, the Gleason score which a physician usually gives to a patient is actually a combination or sum of two numbers. These combined Gleason sums or scores may be determined as follows:

  • In theory, the lowest possible Gleason score is 2 (1 + 1), where both the primary and secondary patterns have a Gleason grade of 1 and therefore when added together their combined sum is 2. However, Gleason grades of 1  and 2 are assigned, today, only to patients who have prostate cancer cells found as a result of a type of surgery called transurethral resection of the prostate (TURP).
  • The lowest Gleason score asigned today to a man who is found to have cancer cells in his prostate on biopsy is 6 (3 + 3). There are complex technical reasons for this, and patients diagnosed before 2002 may have been assigned lower Gleason scores (e.g. 3 + 2 = 5). However, if you are a patient diagnosed today by prostate biopsy there is a very, very high probability that your Gleason score with be 6.
  • Another typical Gleason score might be 7 (4 + 3), where the primary pattern has a Gleason grade of 4 and the secondary pattern has a grade of 3 (or where the primary pattern has a Gleason grade of 3 and secondary pattern has a Gleason grade of 4)
  • Finally, the highest possible Gleason score is 10 (5 + 5), when the primary and secondary patterns both have the most disordered Gleason grades of 5.

What Does the Gleason Score Mean?

The grade of a prostate cancer specimen is very valuable to doctors in helping them to understand how a particular case of prostate cancer can be treated. In general, the time for which a patient is likely to survive following a diagnosis of prostate cancer is related to the Gleason score. A Gleason score of 6 is much better than a Gleaosn score of 10.

However, remember that prostate cancer is a very complicated disease. People with low Gleason scores have been known to fare poorly and men with high Gleason scores have been known to do well. General principles do not always apply to individual patients.

By combining the patient’s Gleason score with his PSA level and the clinical stage estimated by the physician, it is possible to use a variety of nomograms (e.g., the Kattan nomograms) and tables (e.g. the Partin tables) to estimate the likelihood that that patient has localized or locally advanced prostate cancer of different types.

Does the Gleason System Need to be Changed?

As stated above, the standard prostate pathology report provides a Gleason score or sum based on the primary and secondary Gleason grade. On some occasions, a tertiary grade is also reported (usually when there is clear evidence of a small amount of tertiary Gleason grade 5 tissue).

In 2005 an International Consensus Conference of specialized urologic pathologists suggested that the Gleason system for prostatic biopsy reports should be modified to account for the presence of a poorly differentiated or undifferentiated tertiary component. They recommended that the modified approach would sum the most prevalent primary grade and the highest grade. Thus, in the situation with a primary grade 3 and a secondary grade 4 (currently classified as Gleason grade 3 + 4 = 7), cancers with a tertiary grade of 5 would be classified as Gleason grade 3 + 5 = 8. This proposal has not been implemented to date, as the existing system is so well rooted in clinical practice. They also recommended that we should clearly distinguish between a Gleason score of 3 + 4 = 7 by calling this Gleason grade 7a and a Gleason score of 4 +3 = 7 by calling this Gleason score 7b. Why? Because these two pathological categories of prostate cancer appear to behave differently in clinical practice, with Gleason score 4 + 3 = 7b being a more aggressive form of cancer.

The issue of the importance of tertiary Gleason grades may sometimes arise in the prostate cancer literature you learn to read. For example, it is evident in a 2007 paper by Harnden et al. that argues strongly in favor of the modification to Gleason grading described above. It is also important in a 2008 paper by Trpkov et al. that describes the relationship between the presence of tertiary Gleason grade 5 cancer and outcomes after treatment.

Content on this page last reviewed and updated March 18, 2010
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