The histological grading of prostate cancer has undergone many revisions, and for many years the primary system was the Gleason score, itself derived from the Gleason grade. In 2014, the Grade Group was introduced, and care must be taken to not confuse this with the Gleason grade.

The Gleason grade, originally described in 1974, describes the histologic pattern of gland arrangement ². Gleason grade patterns are assigned from 1 to 5:

• 1: well formed glands (least aggressive)
• 5: lacking gland formation (most aggressive)

Most tumors demonstrate two histologic patterns and this is expressed as a Gleason score. The two most common grade patterns seen in a tumor are expressed together and summed. Gleason scores can be expressed as their individual components or as the total Gleason score, eg 3+4=7. The commonest pattern is noted first, hence a Gleason score of 4+3=7 is more aggressive than Gleason score of 3+4=7 (by convention the score numbers and the '+' and '=' symbols are not separated by spaces).

One would expect Gleason scores from 2 to 10, however, Gleason scores less than 6 are not assigned in practice. This leads to patient concern as the lowest possible Gleason score is "6 out of 10". This prompted further revision of prostate cancer grading.

Grade Group stratification was introduced by the International Society of Urological Pathology (ISUP) ³ and has been adopted by the American Joint Committee on Cancer (AJCC). The Gleason score system is compressed into five Grade Groups as per Table 1.

The new Grade Group better reflects prostate cancer biology, with 5-year biochemical risk-free survival after radical prostatectomy of ³:

• Grade Group 1: 96%
• Grade Group 2: 88%
• Grade Group 3: 63%
• Grade Group 4: 48%
• Grade Group 5: 26%

History and etymology

The score is named after an American pathologist Donald Floyd Gleason, (1920-2008) ^4,5. From 1960 to 1964 he reviewed 280 cold cases of prostate carcinoma, from which he was blinded from any clinical details, and identified five histological patterns that were consistently seen. Statisticians at the National Institutes of Health (NIH) amalgamated clinical data with Gleason's work into a scoring system, which they described in 1966. This was validated on a further 4,000 cases by 1974, and the Gleason scale was in ubiquitous usage by the late 1970s ⁵.