Gleason Grading of Prostatic Carcinoma

Proposed Modifications of Gleason Grading

Tertiary Gleason Patterns (Modified Gleason Score)

The Gleason score, by strict definition, only includes the two most common Gleason patterns of the tumor (the primary and secondary patterns). Additional ("tertiary") patterns, including focal patterns, have not been included in the standard Gleason score. When a tumor is essentially all one pattern (e.g. Gleason score 3+3=6) but there is a very focal (<5%) component of pattern 4 or 5, this latter component is also referred to as "tertiary" and it, too, has not been included in the standard Gleason score.

However, it has been demonstrated that a tertiary Gleason pattern 4 or 5 has an adverse impact on prognosis after total prostatectomy. Gleason score 5-6 and 7 tumors with tertiary higher pattern grades progressed more often than tumors without such tertiary patterns. Consequently, we believe that in addition to the standard Gleason score, tertiary patterns 4 or 5 should also be reported.

Although comparable data do not exist for needle biopsy material, when three patterns exist in a biopsy where the highest grade pattern is the least common, we believe that the highest grade pattern should either be mentioned as a tertiary pattern or as a component of a combined Gleason score. The rationale for this is that a small focus of cancer with a high pattern grade on biopsy will usually correlate with a significant amount of high grade cancer in the prostate, and that sampling artifact accounts for its limited nature in the biopsy.

Percentage Gleason Pattern 4/5

Percent Gleason pattern 4/5 in prostatectomy specimens is another proposed addition to Gleason grading. However, percent pattern 4/5 is very predictive for progression only at the extremes (greater than 70% or less than 20% pattern 4/5). More recently, there was not a good correlation between the percent Gleason pattern 4/5 on needle biopsy when compared to the subsequent radical prostatectomy specimen. For example, if there were no pattern 4/5 in the biopsy, 27% of men had >10% pattern 4/5 in the radical prostatectomy specimen. From the practical standpoint, patterns 4 and 3 are often intimately admixed and it is difficult to accurately assess their relative percentages. It seems that percentage of Gleason pattern 4/5 will not likely be performed routinely in the future.