Accurate recognition of Gleason pattern 5 (GP5) prostate adenocarcinoma (PCa) on 
core biopsy (NBX) is critical because it is associated with disease progression 
and the worst clinical outcome. We evaluated 1557 consecutive and prospectively 
collected NBXs to determine the frequency of diagnosis, morphologic subpatterns, 
and their relation to the amount and pattern distribution of GP5 PCa based on 
the 2005 modified Gleason grading system. Tertiary GP5 was upgraded to a 
secondary pattern to derive the final Gleason score. GP5 accounted for 6% of all 
NBXs and 14% of PCa cases. GP5 PCas were associated with high-risk preoperative 
clinical and biopsy characteristics, regardless of the amount of GP5. Most 
patients (85%) with % GP5 greater than 5% of PCa had the final Gleason score of 
9 to 10, compared with % GP5 of 5% or less of PCa (P < .0001). The morphologic 
subpatterns of GP5 PCas were as follows: infiltrating cords (96%), single cells 
(76%), solid sheets (29%), and comedocarcinoma (2%). Infiltrating cords and 
single-cell patterns frequently coexisted (76%). The GP5 was distributed in a 
tertiary (66%), followed by secondary (32%) and primary (2%) components of PCa. 
Infiltrating cords and single cells were the 2 most frequently encountered 
patterns, specifically when GP5 involved 5% or less of PCa and represented 
secondary or tertiary component of PCa. GP5 PCa is a relatively frequent 
presentation in the contemporary NBX practice. Because of its important 
prognostic and therapeutic implications, pathologists must be aware of its 
varied morphologic presentations and to the fact that most cases with GP5 
represent a tertiary component of PCa.