Together with other parameters, it is incorporated into a strategy of prostate cancer staging which predicts prognosis and helps guide therapy.

The system is widely accepted and used for clinical decision making even as it is recognised that certain biomarkers, like ACP1 expression, might yield higher predictive value for future disease course.

Most often, a urologist or radiologist will remove a cylindrical sample (biopsy) of prostate tissue through the rectum (or, sometimes the perineum), using hollow needles, and biomedical scientists in a histology laboratory prepare microscope slides for H&E staining and immunohistochemistry for diagnosis by a pathologist.

[citation needed] After analyzing the tissue samples, the pathologist then assigns a grade to the observed patterns of the tumor specimen.

[citation needed] The pathologist then sums the pattern-number of the primary and secondary grades to obtain the final Gleason score.

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.

[citation needed] The Gleason grade is based on tissue architectural patterns rather than purely cytological changes.

It is a well-defined nodule of single/separate, closely/densely packed, back-to-back gland pattern that does not invade into adjacent healthy prostatic tissue.

Due to this partial separation, fused glands sometimes have a scalloped (think looking at a slice of bread with bite taken out of it) appearance at their edges.

[4] The majority of treatable/treated cancers are of Gleason scores 5-7 and are detected due to biopsy after abnormal digital rectal exam or prostate specific antigen evaluation.

The cancer is typically located in the peripheral zone usually the posterior portion, explaining the rationale of performing the digital rectal exam.

Although some evidence suggests that prostate cancers will become more aggressive over time, Gleason scores typically remain stable for several years.

[4] The Gleason scores then become part of the TNM or Whitmore-Jewett prostate cancer staging system to provide prognosis.

[8][9] In 2005 the International Society of Urological Pathology altered the Gleason system, refining the criteria and changing the attribution of certain patterns.

[4] It has been shown that this "modified Gleason score" has higher performance than the original one, and is currently assumed standard in urological pathology.

Patients who are told their Gleason score is 6 out of 10 may interpret that they have a more aggressive intermediate cancer and experience greater anxiety.

A 5-point Gleason Grade grouping similar to those such as PI-RADS used with prostate MRI evaluations was proposed to denote prognostically distinct stratification.