**3. Development of the Gleason score**

The Gleason grading system for prostate adenocarcinoma originated in the 1960s from a randomized prospective study performed at the Veterans Administration that included nearly 3000 patients. Dr. Donald Gleason detailed and summarized the histological growth patterns (grades) of prostate adenocarcinoma, and the correlation with clinical data such as staging and prognosis were analyzed.

At the 2014 International Society of Urological Pathology Consensus Conference, a new prostate adenocarcinoma grading system was developed from the latest Gleason scoring system that was last revised in 2005, which included a new system of Grade Groups from Gleason scores 1–5, as follows: [6].

Grade Group 1: Gleason score ≤ 6; only individual discrete well-formed glands. Grade Group 2: Gleason score 3 + 4 = 7; predominantly well-formed glands with lesser components of poorly formed/fused/cribriform glands.

Grade Group 3: Gleason score 4 + 3 = 7; predominantly poorly formed/fused/ cribriform glands with lesser component of well-formed glands

• For cases with >95% poorly formed/fused/cribriform glands or lack of glands on a core or at radical prostatectomy, the component of <5% well-formed glands is not factored into the grade.

Grade Group 4: Gleason score 4 + 4 = 8, 3 + 5 = 8, 5 + 3 = 8


Grade Group 5: Gleason score 9–10; lack gland formation (or with necrosis) with or without poorly formed/fused/cribriform glands.
