Interobserver reproducibility of Gleason grading of prostatic carcinoma: General pathologists

Only a few large studies of interobserver reproducibility of Gleason grading of prostatic carcinoma exist. Thirty-eight biopsies containing prostate cancer were distributed for Gleason grading to 41 general pathologists in Georgia. These cases had "consensus" Gleason grade groups (2-4, 5-6, 7, and 8-10) that were agreed on by at least 7 of 10 urologic pathologists. The overall kappa (κ) coefficient for interobserver agreement for these 38 cases was 0.435, barely moderate agreement, with a κ range from 0.00 to 0.88. There was consistent undergrading of Gleason scores 5-6 (47%), 7 (47%) and, to a lesser extent, 8-10 (25%). In cases with consensus primary patterns, there was consistent undergrading of patterns 2 (32%), 3 (39%), and 5 (30%). Pattern 2 was often (17%) mistaken for pattern 3. Pattern 4 was often undergraded (21%) and also mistaken for pattern 5 (17%). The most significant (P < .005) demographic factor associated with better interobserver agreement was having learned Gleason grading at a meeting or course. We believe that Gleason grading can be learned to a satisfactory level of interobserver reproducibility and have undertaken additional studies that support this belief.