Inherent Grading Characteristics of Individual Pathologists Contribute to Clinically and Prognostically Relevant Interobserver Discordance Concerning Broders' Grading of Penile Squamous Cell Carcinomas

Introduction: We assessed the reproducibility and prognostic impact of the Broders' grading system (BGS) in a cohort of 147 patients with surgically treated penile squamous cell carcinomas. Materials and Methods: Conventionally stained histology slides were graded according to the BGS in two rounds by two study pathologists. Reproducibility was assessed using ĸ statistics. Multivariable analyses were calculated to predict cancer-specific survival (CSS). The ‘mean grade' per pathologist per round was calculated by allocating grade points to each study case (G1-G4: 1-4 points) and dividing the sum of all grade points by the number of cases examined. Results: The BGS showed substantial interobserver variation (59-87% with ĸ = 0.38-0.69) but almost perfect intraobserver reproducibility (91% with ĸ = 0.86 and 96% with ĸ = 0.94, respectively). The ‘mean grade' per pathologist remained nearly constant in both rounds of examination (differences ≤0.05 grade points) but differed between the two pathologists (up to 0.4 grade points). In multivariable analyses, the prognostic impact of the BGS in terms of CSS was strongly pathologist-dependent. Conclusions: Clinically and prognostically relevant interobserver discordance concerning the BGS seems, at least in part, to be attributable to inherent ‘aggressive' versus ‘reserved' grading characteristics of individual pathologists.