Pathologists review biopsy tissue and assign it a Gleason grade based on the appearance of the cells. If cancer is present, it will be assigned two Gleason grades ranging from 1 to 5. The primary grade, or first number shown, is the most common Gleason pattern (grade) found in the biopsy. The second number is the second most common Gleason pattern (grade).  These two numbers are added together for a Gleason score. Gleason scores range from 2 to 10 with most prostate cancer ranging from 6 to 10. An example Gleason score is 3+4=7. In this example, 3 is the primary pattern, and 4 is the secondary. When added together they equal 7.

Another term you may hear regarding Gleason scores is Grade Groups. Gleason scores have been divided into groups ranging from 1 to 5. Gleason score and Gleason grades determine the Gleason group.

Gleason Group Break Down

Grade group 1: Gleason score = 6 (or less) and Gleason pattern = 3+3

Grade group 2: Gleason score = 7 and Gleason pattern = 3+4

Grade group 3: Gleason score = 7 and Gleason pattern = 4+3

Grade group 4: Gleason score = 8 and Gleason pattern = 4+4, 3+5, 5+3

Grade group 5: Gleason score = 9 or 10 and Gleason pattern = 4+5, 5+4, 5+5

Limitations of Gleason Scoring:

Gleason scores play a vital role in determining treatment decisions. First developed in the 1970s, Gleason scores have been used to assess the aggressiveness of patient’s prostate cancer. Unfortunately, errors when determining biopsy Gleason score are common. Gleason grading and scoring are largely subjective, and not all pathologists may agree on a Gleason grade, especially on small tissue samples obtained at biopsy. Therefore, variation between pathologists does occur.