High-intensity Focused Ultrasound (HIFU) as salvage therapy for radio-recurrent prostate cancer: predictors of disease response.

BACKGROUND Some men with localized radio-recurrent prostate cancer may benefit from salvage high-intensity focused ultrasound (HIFU). Herein, we describe oncologic outcomes and predictors of disease response after salvage whole gland HIFU from our prospective cohort. MATERIALS AND METHODS Patients with localized radio-recurrent prostate cancer were prospectively enrolled from January 2005 to December 2014. Participants had to meet both biochemical and histological definitions of recurrence. Exclusion criteria included the receipt of prior salvage therapy, presence of metastatic disease, and administration of ADT in the 6-months prior to enrollment. Participants were treated with a single session of whole-gland HIFU ablation with the AblathermTM device (EDAP, France). The primary endpoint was recurrence-free survival (RFS), defined as a composite endpoint of PSA progression (Phoenix criteria), 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 (TRUS biopsy grade, number of study entry TRUS biopsy cores positive, palpable disease at study enrollment, pre-HIFU PSA, an undetectable post-HIFU PSA nadir, and receipt of prior hormone therapy). 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 4.02ng/ml. Median time to PSA nadir was 3 months after treatment and median post-HIFU PSA nadir was 0.04ng/ ml. Median 2-year and 5-year RFS was 66.3% and 51.6% respectively. Of our 6 pre-specified predictors, 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). One participant underwent an intervention for a urethral stricture. No participants developed osteitis pubis or rectourethral fistulae. CONCLUSIONS Salvage HIFU allows for disease control in selected patients with localized radio-recurrent prostate cancer. An undetectable PSA nadir serves as an early predictor of disease response.