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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 staining and Immunohistochemistry for diagnosis by a pathologist. If the prostate is surgically removed, a pathologist will slice the prostate for a final examination.
A pathologist microscopically examines the biopsy specimen for certain "Gleason" patterns. These Gleason patterns are associated with the following features:
In the present form of the Gleason system, prostate cancer of Gleason patterns 1 and 2 are rarely seen. Gleason pattern 3 is by far the most common.
A pathologist then assigns a grade to the observed patterns of the tumor specimen.
The pathologist then sums the pattern-number of the primary and secondary grades to obtain the final Gleason score. If only two patterns are seen, the first number of the score is that of the tumor's primary grade while the second number is that of the secondary grade, as described in the previous section. If three patterns are seen, the first number of the score would be the primary grade and the second number the pattern with the highest grade. For example, if the primary tumor grade was 2 and the secondary tumor grade was 3 but some cells were found to be grade 4, the Gleason score would be 2+4=6. This is a slight change from the pre-2005 Gleason system where the second number was the secondary grade (i.e., the grade of the second-most common cell line pattern). There could be a Gleason score of 3+4 with a tertiary component of pattern 5 - this would be considered to be more aggressive than a prostate cancer that was Gleason score of 3+4 with no tertiary pattern 5. However, the full significance of the tertiary component on the aggressiveness of a cancer is debatable.
Gleason scores range from 2 to 10, with 2 representing the most well-differentiated tumors and 10 the least-differentiated tumors. Gleason scores have often been categorized into groups that show similar biologic behavior: low-grade (well-differentiated), intermediate-grade, moderate to poorly-differentiated or high-grade. More recently, an investigation of the Johns Hopkins Radical Prostatectomy Database (1982-2011) led to the proposed reporting of Gleason grades and prognostic grade groups as: Gleason score ≤ 6 (prognostic grade group I); Gleason score 3+4=7 (prognostic grade group II); Gleason score 4+3=7 (prognostic grade group III); Gleason score 4+4=8 (prognostic grade group IV); Gleason scores 9-10 (prognostic grade group V). Prostate cancers with a Gleason score ≤ 6 usually have rather good prognoses.
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.