Table 1.

Comparison of the classical and International Society of Urological Pathology modified Gleason grading system

Classical Gleason system (14)	2005 ISUP modified Gleason system (15)
Pattern 1: Well-differentiated small, uniform, and closely packed glands in tight circumscribed masses	Pattern 1: Circumscribed nodule of closely packed, separate, uniform round-oval, medium-sized glands (generally larger than pattern 3)
Pattern 2: Similar to pattern 1, with moderate variation in size and shape of glands and some cellular atypia; glands more loosely packed but still relatively circumscribed	Pattern 2: Similar to pattern 1, but more loosely packed glands with minimal infiltration at edges of tumor nodule and mild glandular irregularity
Pattern 3: Very small infiltrating glands with marked irregularity of size and shape but generally retaining individual glandular differentiation; individual cells invading stroma away from circumscribed glandular masses; papillary and cribriform arrangements ranging from small to large but maintaining smooth rounded edges	Pattern 3: Small discrete glandular acini (generally smaller than patterns 1 and 2) with marked variation in size and shape and that typically infiltrate amongst nonneoplastic prostatic acini; smoothly circumscribed small cribriform glandular units
Pattern 4: Raggedly infiltrating fused glands that coalesce and branch and are no longer single and separate; glands with large clear cells resembling hypernephroma	Pattern 4: Fused microacinar glands and ill-defined glands with poorly formed glandular lumina; large cribriform glandular units or cribriform glands with irregular borders; hypernephromatoid, ductal tumors
Pattern 5: Infiltrative, very poorly differentiated cells arranged in solid or diffuse masses or individual cells with essentially no glandular differentiation; includes signet ring cell morphology and comedocarcinoma	Pattern 5: Tumor cells with essentially no glandular differentiation arranged in solid sheets, cords, or single cells; comedocarcinoma with central necrosis surrounded by papillary, cribriform, or solid cell masses
Gleason scoring
Gleason score obtained by adding together the most prominent pattern (primary) with the second most prominent pattern (secondary)	Similar to classical, with following exceptions: Gleason scores 2–4 should rarely (if ever) be assigned to tumors on biopsies
Same scoring method used for prostatectomy and biopsy	On biopsies, the Gleason score should be obtained by adding together the most prominent pattern (primary) with the highest remaining grade pattern (even if tertiary or <5%)