Interobserver Reproducibility of Percent Gleason Pattern 4 in Prostatic Adenocarcinoma on Prostate Biopsies

In the WHO Classification of Tumours of the Urinary System and Male Genital Organs published in 2016, it was officially recommended that the percent of Gleason pattern 4 (GP4) be reported on pathology reports to better reflect the extent in Gleason score 7 tumors. In this study we assessed the reproducibility of reporting GP4 on prostate biopsies. We analyzed prospectively 422 cores containing GP4 from our consult cases over a period of 2.5 months. The percent pattern 4 was assigned to all the cases in 10% increments from 0% to 100% (with the addition of 5%) by 1 of 4 fellows in urological pathology and by the expert urological pathologist. Out of 422 cores, 32% were an exact match and 75% were within ±10% (weighted κ [κW] value 0.67). Cases were further stratified on the basis of (1) scattered versus clustered GP4 in the background of Gleason pattern 3, (2) continuous versus discontinuous tumor involvement, (3) cribriform/glomeruloid pattern only versus poorly formed/fused pattern versus mixed cribriform and poorly formed/fused pattern, and (4) total tumor involvement of the core (≤10% vs. >10% of the core). No significant differences were observed in the first 3 variables. However, in cases with ≤10% involvement of the core, 61% were within ±10% (κW=0.50) compared with cases with >10% involvement of the core, in which 78% were within ±10% (κW=0.70). In summary, we showed that assessment of percent GP4 was relatively reproducible, with substantial agreement within ±10% in cases. However, with <10% involvement of the core, it was more difficult to assess in smaller foci, with only moderate agreement. Given that in a small focus only a few glands of a given pattern can markedly affect the percent GP4, consideration should be given to not recording percent GP4 in small foci of Gleason score 7 tumors on needle biopsy.