Association of Brachytherapy Boost with Overall Survival for Gleason 9-10 Prostate Cancer: The Impact of Primary versus Secondary Pattern 5.

PURPOSE: The addition of a brachytherapy (BT) boost to external beam radiotherapy (EBRT) reduces recurrence risk in men with high-risk prostate cancer (PCa) and may reduce PCa-mortality for Gleason grade group 5 (GG5). Whether the extent of pattern five, a risk factor for distant metastases, impacts the benefit of a BT boost is unclear. METHODS: Men with localized GG5 PCa treated with (1) EBRT or (2) EBRT+BT between 2010 and 2016 were identified in the National Cancer Database. EBRT monotherapy group received conventionally fractionated (1.8-2.0 Gy per fraction) ≥74 Gy or moderately hypofractionated (2.5-3.0 Gy per fraction) ≥60 Gy. EBRT + BT group received conventionally fractionated ≥45 Gy or moderately hypofractionated ≥37.5 Gy, and either LDR or HDR BT. All patients received concomitant ADT; none received chemotherapy, immunotherapy, or surgery. OS was compared using Kaplan-Meier, log-rank test, and multivariable Cox proportional hazards in the overall cohort, followed by subgroups based on primary versus secondary pattern 5. Propensity score- and exact-matching was used to corroborate results. RESULTS: A total of 8260 men were eligible: EBRT alone (89%) versus EBRT + BT (11%). 5-year OS for EBRT versus EBRT + BT was 76.3% and 85.0%, respectively (p = 0.002; multivariable adjusted HR 0.84, 95% CI 0.65-0.98; p = 0.04). These results remained consistent after propensity score and exact matching. The OS advantage of a BT boost was more prominent in men with Gleason 4 + 5 PCa (p = 0.001) and not observed in men with Gleason 5 + 5 or 5 + 4 PCa. CONCLUSIONS: Extent of pattern five may be useful in appropriately selecting men for EBRT+BT and should be considered as a pre-randomization stratification variable for future clinical trial design.