Gleason Grading System
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 biomedical scientists in a Histology laboratory prepare microscope slides for H&E and Immunohistochemistry for diagnosis by a pathologist. After a prostate is removed in surgery, a pathologist will slice the prostate for a final examination.
Grades and scores 
The pathologist assigns a Gleason score based on the sum of two numbers: the first number is the grade of the most common tumor pattern, the second number is the highest grade cells found in the tumour. For example, if the most common tumor pattern was grade 3, but some cells were found to be grade 4, the Gleason Score would be 3+4 = 7. This is a slight change to the pre-2005 Gleason system where the second number was the grade of the second most common cell line. 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 present form of the Gleason system, prostate cancer of Gleason pattern 1 and 2 are almost never seen, and by definition are almost never seen on biopsy. Gleason pattern 3 is by far the most common. Thus a Gleason score 3+3=6 cancer is to be regarded as LOWEST grade seen in practice, and indeed this cancers have usually rather good prognosis.
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.
The scoring system is named after Donald Gleason, a pathologist at the Minneapolis Veterans Affairs Hospital who developed it with other colleagues at that facility in the 1960s. In 2005 the Gleason system was altered by the International Society of Urological Pathology. The criteria were refined and the attribution of certain patterns changed . It has been shown that this 'modified Gleason score' has higher performance than the original one, and is currently assumed standard in urological pathology. In this form, it remains an important tool.
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- Epstein JI, Allsbrook WC Jr, Amin MB, Egevad LL; ISUP Grading Committee. The 2005 International Society of Urological Pathology (ISUP) Consensus Conference on Gleason grading of prostatic carcinoma. Am J Surg Pathol 2005;29(9):1228-42.
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1. Epstein JI, Allsbrook WC Jr, Amin MB, Egevad LL; ISUP Grading Committee. The 2005 International Society of Urological Pathology (ISUP) Consensus Conference on Gleason Grading of Prostatic Carcinoma. Am J Surg Pathol. 2005 ;29(9):1228-42
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