The 2005 International Society of Urological Pathology (ISUP) Consensus Conference on Gleason Grading of Prostatic Carcinoma.

Donald F. Gleason in 1966 created a unique grading system for prostatic carcinoma based solely on the architectural pattern of the tumor. Another innovative aspect of this system was, rather than assigning the worst grade as the grade of the carcinoma, the grade was defined as the sum of the two most common grade patterns and reported as the Gleason score. The original description of this system, based on a study of 270 patients from the Minneapolis Veterans Administration Hospital, is seen in Table 1. Initially, Gleason intended to classify carcinomas into four patterns, but a small group of distinctive tumors (clear cell) was observed and they were placed in a separate fifth category (pattern 4). Certain aspects of the original Gleason system would be interpreted differently in today’s practice. The cribriform pattern described as a component of Gleason’s original patterns 2 and 3 would today typically be considered higher grade. Individual cells listed under Gleason’s original pattern 3 would also be currently assigned a higher grade. Pattern 4 has become significantly expanded beyond Gleason’s original description of tumors with clear cytoplasm that resembled renal cell carcinoma (Table 1). By 1974, Gleason and theVeteransAdministrationCooperative Urological Research Group expanded their study to 1032 men. Gleason pattern 4 was described in a figure legend as ‘‘raggedly infiltrating, fused-glandular tumor, frequently with pale cells, may resemble hypernephroma of kidney.’’ The Gleason system was further refined by Mellinger in 1977 when the papillary and cribriform tumor under Gleason pattern 3 was described as having a ‘‘smooth and usually rounded edge.’’ These modifications of the Gleason system are depicted in Table 1. In describing the breakdown of Gleason patterns among 2911 cases, Gleason pattern 1 was seen in 3.5%; pattern 2 in 24.4%; pattern 3 in 87.7%; pattern 4 in 12.1%; and pattern 5 in 22.6%. These percentages added up to approximately 150% because 50% of the tumors showed at least two different patterns. In 1977, Gleason provided additional comments concerning the application of the Gleason system. ‘‘Grading is performed under low magnification (40–1003).’’ He also stated ‘‘an occasional small area of fused glands did not change a pattern 3 tumor to pattern 4. A small focus of disorganized cells did not change a pattern 3 or 4 tumor to pattern 5.’’ The only comment relating to tertiary patterns was ‘‘occasionally, small areas of a third pattern were observed.’’