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.