Purpose: The GG (Grade Group) system was introduced in 2013. Data from academic centers suggest that GG better distinguishes between prostate cancer risk groups than the Gleason score (GS) risk groups. We compared the performance of the 2 systems to predict pathological/recurrence outcomes using data from the MUSIC (Michigan Urological Surgery Improvement Collaborative).
Materials and methods: Patients who underwent biopsy and radical prostatectomy in the MUSIC from March 2012 to June 2017 were classified according to GG and GS. Outcomes included the presence or absence of extraprostatic extension, seminal vesical invasion, positive lymph nodes, positive surgical margins and time to cancer recurrence (defined as postoperative prostate specific antigen 0.2 ng/ml or greater). Logistic and Cox regression models were used to compare the difference in outcomes.
Results: A total of 8,052 patients were identified. When controlling for patient characteristics, significantly higher risks of extraprostatic extension, seminal vesical invasion and positive lymph nodes were observed for biopsy GG 3 vs 2 and for GG 5 vs 4 (p <0.001). Biopsy GGs 3, 4 and 5 also showed shorter time to biochemical recurrence than GGs 2, 3 and 4, respectively (p <0.001). GGs 3, 4 and 5 at radical prostatectomy were each associated with a greater probability of recurrence compared to the next lower GG (p <0.001). GG (vs GS) had better predictive power for extraprostatic extension, seminal vesical invasion, positive lymph nodes and biochemical recurrence.
Conclusions: GG at biopsy and radical prostatectomy allows for better discrimination of recurrence-free survival between individual risk groups than GS risk groups with GGs 2, 3, 4 and 5 each incrementally associated with increased risk.