The Gleason system (named after the pathologist who invented it) is a widely used method for classifying, or grading, prostate cancer tissue.(4) Using samples obtained from the prostate gland by biopsy or following a prostatectomy the pathologist looks at how the cancer cells are arranged.
Cells appearing close to normal and well organised are well differentiated and in general slow growing. Prostate cancer cells that are more disorganised and chaotic, forming abnormal or bizarre patterns, are poorly differentiated and are usually more aggressive.
Each component (the differentiation and the pattern) is given a numerical value from 1 to 5. The sum of the two most frequent patterns are assessed and the grades are added together to give an overall Gleason score, ranging between 2 and 10. The lower the score, the lower the grade of the cancer. The higher the score, the higher the grade.
The majority of prostate cancers are diagnosed using biopsy samples. However, there are several problems that arise when applying Gleason grading to needle core biopsies compared with radical prostatectomy specimens. Biopsy samples are often too small - making it difficult to recognise low grade cellular patterns. As a result the biopsy samples are almost always given a Gleason score of 3 or higher. This means that the total Gleason score ranges from 6 to 10, and that the lower numbers (2–5) are usually not seen.
- Gleason score 6 - Well differentiated or low grade
- Gleason score 7 - Moderately differentiated or moderate grade
- Gleason score 8–10 Poorly differentiated or high grade.
The Gleason score provides useful information about prognosis. A Gleason score above 8 is associated with a risk of more rapid disease progression, increased metastatic potential and decreased survival. (3),(5)