Variance of Tumor Grade at Radical Prostatectomy With Assessment of Each Tumor Nodule Versus Global Grading

Abstract

Context.— Multifocal prostate cancer at radical prostatectomy (RP) may be graded with assessment of each individual tumor nodule (TN) or global grading of all TNs in aggregate. Objective.— To assess case-level grade variability between these 2 grading approaches. Design.— We reviewed 776 RPs with multifocal prostate cancer with 2 or more separate TNs of different Grade Groups (GGs). Two separate grades were assigned to each RP: one based on the TN with the highest grade and a global grade based on the Gleason pattern volumes for all TNs. We then compared the results of these 2 methods. Results.— The case-level grade changed by 1 or more GGs between the 2 grading methods in 35% (132 of 374) of GG3 through GG5 cases. Twelve percent (37 of 309) of GG2 cases with Gleason pattern 4 more than 5% based on individual TN grading decreased their Gleason pattern 4 to less than 5% based on the global approach. Minor tertiary pattern 5 (Gleason pattern 5 <5%) was observed in 6.8% (11 of 161) of GG4 (Gleason score 3 + 5 = 8 and 5 + 3 = 8) and GG5 cases with global grading. The risk of grade discrepancy between the 2 methods was associated with the highest-grade TN volume (inverse relationship), patient age, and number of TNs (P < .001, P = .003, and P < .001, respectively). Conclusions.— The global grading approach resulted in a lower grade in 35% of GG3 through GG5 cases compared with grading based on the highest-grade TN. Two significant risk factors for this discrepancy with a global grading approach occur when the highest-grade TN has a relatively small tumor volume and with the higher number of TNs per RP. The observed grade variability between the 2 grading schemes most likely limits the interchangeability of post-RP multi-institutional databases if those institutions use different grading approaches.