The Gleason Grading system is used to help evaluate the prognosis of men with prostate cancer. Together with other parameters, it is incorporated into a strategy of prostate cancer staging which predicts prognosis and helps guide therapy. A Gleason score is given to prostate cancer based upon its microscopic appearance. Cancers with a higher Gleason score are more aggressive and have a worse prognosis.
Most often, a urologist or radiologist will remove a cylindrical sample (biopsy) of prostate tissue through the rectum, using hollow needles, and prepare microscope slides. After a prostate is removed in surgery, a pathologist will slice the prostate for a final examination.
Grades and scores
The pathologist assigns a grade to the most common tumor pattern, and a second grade to the next most common tumor pattern. The two grades are added together to get a Gleason Score. For example, if the most common tumor pattern was grade 3, and the next most common tumor pattern was grade 4, the Gleason Score would be 3+4 = 7. The Gleason Grade is also known as the Gleason Pattern, and the Gleason Score is also known as the Gleason Sum. The Gleason Grade or Gleason Pattern ranges from 1 to 5, with 5 having the worst prognosis. The Gleason Score ranges from 2 to 10, with 10 having the worst prognosis. For Gleason Score 7, a Gleason 4+3 is a more aggressive cancer than a Gleason 3+4. Also, there is not really any difference between the aggressiveness of a Gleason Score 9 or 10 tumor.
Patterns 1 through 5
Gleason patterns are associated with the following features:
- Pattern 1 – The cancerous prostate closely resembles normal prostate tissue. The glands are small, well-formed, and closely packed.
- Pattern 2 – The tissue still has well-formed glands, but they are larger and have more tissue between them.
- Pattern 3 – The tissue still has recognizable glands, but the cells are darker. At high magnification, some of these cells have left the glands and are beginning to invade the surrounding tissue.
- Pattern 4 – The tissue has few recognizable glands. Many cells are invading the surrounding tissue
- Pattern 5 – The tissue does not have recognizable glands. There are often just sheets of cells throughout the surrounding tissue.
In the United Kingdom, prostate cancer of Gleason pattern 1 and 2 are almost never seen. Gleason pattern 3 is by far the most common.
Primary, secondary, and tertiary
A pathologist examines the biopsy specimen and attempts to give a score to the two patterns.
- First called the primary grade, represents the majority of tumor (has to be greater than 50% of the total pattern seen).
- Second – a secondary grade – relates to the minority of the tumor (has to be less than 50%, but at least 5%, of the pattern of the total cancer observed).
These grades are then added to obtain the final Gleason score.
Increasingly, pathologists provide details of the “tertiary” component. This is where there is a small component of a third (generally more aggressive) pattern. So there could be a Gleason 3+4 with a tertiary component of pattern 5 – this would be considered to be more aggressive than a prostate cancer that was Gleason 3+4 with no tertiary pattern 5. Although it is debatable as to what the full extent the tertiary component has on the aggressiveness of a cancer.
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