[1052] Downgrading of the Biopsy Gleason Score in Prostatectomy Specimens

Kilian M Treurniet, Dominique Trudel, Jenna Sykes, Andrew J Evans, Theo van der Kwast. Leiden University Medical Centre, Leiden, Netherlands; University Health Network, Toronto, Canada

Background: Downgrading a prostate cancer from a Gleason score 7 on a biopsy to a Gleason score 6 on the radical prostatectomy (RP) could mean that a patient has been exposed to excess treatment and morbidity. The introduction of the 2005 ISUP Gleason grading system may have changed the frequency and the causes of downgrading.
Design: Our objective was to assess the contemporary frequency of downgrading from a biopsy Gleason score 7 to a Gleason score 6 or lower at RP in a Canadian referral centre and the possible causes of this phenomenon. We identified all cases of prostate cancers biopsies that were graded as Gleason score 7 between 2008 and 2011 and their corresponding RP specimens, provided that both the biopsy and the RP were performed at our institution. Data was extracted from the diagnostic reports and an experienced genito-urinary pathologist reviewed the biopsy and the prostatectomy slides from the cases that were downgraded from a Gleason score 7 at biopsy to a Gleason score 6 or lower at RP. Using the student t-test, differences between the downgraded and non-downgraded cases with regard to pathologic features were assessed in both the pre- and post-review data. Binary logistic regression was used to identify possible predictors for downgrading.
Results: A total of 327 biopsies with Gleason score 7 and matched RP were identified. According to pathology reports, 8.8% of these were downgraded. After slide review, this frequency decreased to 4.5%. For originally reported and post-review cases, respectively 76% and 71.4% of the downgraded cases represented RP Gleason score 6 with a tertiary grade. Agreement for presence of tertiary grade 4 in RP was moderate between pre and post-review data (kappa 0.53). The predominant Gleason 4 patterns found in downgraded cases were ill-formed and small fused glands. In the pre-review dataset, both the number of cores with high-grade component (OR=0.56, 95% confidence interval (CI) 0.39-0.80, p=0.001) and the number of cores containing cancer were found to be predictive for downgrading (OR=1.23, 95% CI 1.01-1.50, p=0.042). In the post-review dataset, the only predictor of downgrading was the number of biopsy cores with a high-grade component (OR=0.20, 95% CI 0.07-0.60, p=0.004).
Conclusions: The frequency of Gleason score 7 in biopsies subsequently downgraded in RP is low and could be attributed in most cases to the presence of a tertiary Gleason grade 4 pattern found in the RP specimen. Further, the number of biopsy cores with a high-grade component was found to be the best negative predictor of downgrading.
Category: Genitourinary (including renal tumors)

Wednesday, March 6, 2013 1:00 PM

Poster Session VI # 136, Wednesday Afternoon

 

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