High-intensity focused ultrasound (HIFU) as salvage therapy for radio-recurrent prostate cancer: Predictors of disease response.

135 Background: Some patients with localized radio-recurrent prostate cancer (PCa) may have long-term recurrence-free (RFS) survival with salvage high-intensity focused ultrasound (HIFU). In this study, we describe our previously unreported oncologic outcomes and predictors of disease response after salvage HIFU. Methods: Participants were prospectively enrolled in this study from January 2005 to December 2014 if they had localized radio-recurrent prostate cancer. Participants had to meet both biochemical (PSA nadir+ 2ng/ml) and histologic (positive biopsy) definitions of recurrence. Study exclusion criteria included the receipt of prior salvage therapy, presence of metastastatic disease, and receipt of ADT in the 6-months prior to enrollment. Participants were treated with a single session of whole-gland HIFU ablation with the Ablatherm device (EDAP, France). The primary endpoint of this study was RFS, defined as a composite endpoint of PSA progression (PSA nadir + 2 ng/ml), receipt of any further salvage therapy, receipt of ADT, clinical progression, or death. Kaplan-Meier survival analysis was used to determine the primary end-point and stratifications were used to determine the significance of 6 pre-specified predictors of improved RFS (undetectable PSA nadir, low TRUS biopsy grade, >3 TRUS biopsy cores positive, pre-HIFU PSA<4ng/ml, receipt of prior ADT and presence of pre-HIFU palpable disease). Survival analysis was performed on participants with a minimum of 1-year follow-up. Results: Twenty-four participants were eligible for study inclusion with a median follow-up of 31.0 months. Median PSA at study entry was 4.02 ng/ml. Median time to PSA nadir was 3 months after treatment and median post-HIFU PSA nadir was 0.04 ng/ml. 2-year and 5-year RFS were 66.3% and 51.6% respectively. An undetectable PSA nadir was the only significant predictor of improved RFS (HR 0.07, 95% CI 0.02-0.29, log-rank P<0.001). No participants developed a rectourethral fistula. Conclusions: Salvage HIFU allows for disease control in select patients with localized radio-recurrent prostate cancer. An undetectable PSA nadir serves as an early predictor of disease response.