Downgrading of biopsy based Gleason score in prostatectomy specimens.

Aims: To assess the frequency and possible causes of downgrading from a Gleason score (GS) 7 at biopsy to a GS ≤6 at radical prostatectomy (RP) in a Canadian referral centre.
Methods: Data were extracted from diagnostic reports of inhouse biopsies and matching prostatectomy specimens from 2008 to 2011 with a GS 7 at biopsy. Biopsies and corresponding prostatectomy specimens of downgraded cases were reviewed. Pathological features were assessed and possible predictors for downgrading were identified.
Results: Based on pathology reports, 29 (8.9%, 95% CI 5.8% to 11.9%) of the 327 eligible cases were downgraded from biopsy GS 7 to RP GS 6, 72% of them representing a GS ≤6 with tertiary grade 4 at RP. Agreement at review of downgraded RP specimens for Gleason grading was fair and of borderline significance (κ=0.34, 95% CI -0.01 to 0.68, p=0.055) with 65% agreement for tertiary grade. The predominant Gleason grade 4 pattern found in the downgraded biopsies was ill-formed glands. The number of cores with Gleason grade 4 component was found to be the strongest negative predictor of downgrading (prereview OR=0.56 (95% CI 0.39 to 0.80, p=0.002), postreview OR=0.19 (95% CI 0.07 to 0.52, p=0.001)).
Conclusions: The frequency of GS 7 in biopsies subsequently downgraded in RP is low and is associated with International Society of Urological Pathology modified Gleason grade 4 patterns. Downgrading could be attributed in most cases to the presence of a tertiary Gleason grade 4 pattern in the RP specimen. Inter-observer agreement for the presence of tertiary grade 4 in RP specimens is moderate.