Gleason score
Gleason 1 Gleason pattern 1 is the most well differentiated tumor pattern. 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. The glands are round to oval shaped and proportionally large, comparing them to Gleason pattern 3 tumors, and are approximately equal in size and shape to one another. Gleason 2 Gleason 2 are fairly well circumscribed nodules of single, separate glands. However, the glands are looser in arrangement and not as uniform as in pattern 1. Minimal invasion by neoplastic glands into the surrounding healthy prostate tissue may be seen. Similar to Gleason 1, the glands are usually larger than those of Gleason 3 patterns, and are round to oval in shape. Thus the main difference between Gleason 1 and 2 is the density of packing of the glands seen and invasion is possible in Gleason 2, not in Gleason 1 by definition. Gleason 3 Gleason 3 is a clearly infiltrative neoplasm, with extension into adjacent healthy prostate tissue. The glands alternate in size and shape, and are often long/angular. They are usually small/micro-glandular in comparison to Gleason 1 or 2 grades. However, some may be medium to large in size. The small glands of Gleason 3, in comparison to the small and poorly defined glands of pattern 4, are distinct glandular units. Mentally you could draw a circle around each of the glandular units in Gleason 3. Gleason 4 Gleason pattern 4 glands are no longer single/separated glands like those seen in pattern 1-3. They look fused together, difficult to distinguish, with rare lumen formation vs Gleason 1-3 which usually all have open lumens (spaces) within the glands, or they can be cribriform-(resembling the cribriform plate/similar to a sieve. An item with many perforations). Fused glands are chains, nests, or groups of glands that are no longer entirely separated by stroma-(connective tissue that normally separates individual glands in this case). Fused glands contain occasional stroma giving the appearance of "partial" separation of the glands. 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. Gleason 5 Neoplasms have no glandular differentiation (thus not resembling normal prostate tissue at all). It is composed of sheets (groups of cells almost planar in appearance (like the top of a box), solid cords (group of cells in a rope like fashion running through other tissue/cell patterns seen), or individual cells. You should not see round glands with lumenal spaces that can be seen in the other types that resemble more the normal prostate gland appearance.
