Focal salvage high-intensity focused ultrasound in radiorecurrent prostate cancer

Objective: To assess short- to medium-term cancer control rates and side effects of focal salvage high- intensity focused ultrasound (HIFU).

Materials and methods: A retrospective registry analysis identified 150 men who underwent focal salvage HIFU (FS-HIFU) (Sonablate 500) between November 2006 and August 2015. Metastatic disease was excluded by nodal assessment on the pelvic MRI, a radioisotope bone scan and positron-emission tomography (PET) imaging (choline-18F-fluorodeoxyglucose PET or choline PET-CT). In our current clinical practice, metastatic disease must be excluded by both choline PET and bone scan. Localization of cancer was carried out using multiparametric MRI of the prostate (T2-weighted, diffusion-weighted and dynamic contrast-enhanced imaging) with systematic or template prostate mapping biopsies. The primary outcome was a composite failure incorporating biochemical failure (BCF) and/or positive localized or distant imaging results and/or positive biopsy and/or systemic therapy and/or metastases/prostate cancer-specific death. The secondary outcome was BCF using the Phoenix-ASTRO definition (prostate-specific antigen [PSA] nadir + 2 ng/mL). We used Kaplan-Meier analysis and Cox proportional hazards regression to quantify the effect of the determinants on the endpoints.

Results: The mean (standard deviation [sd]) patient age at focal salvage HIFU was 69.8 (6.1) years and the median (interquartile range [IQR]) PSA pre-focal salvage HIFU was 5.5 (3.6-7.9) ng/mL. The median (IQR) follow-up was 35 (22-52) months. Patients were classified as having low- 2.7% (4/150), intermediate- 39.3% (59/150) and high-risk disease 41.3% (62/150) according to D'Amico classification, prior to focal salvage HIFU. Composite failure occurred in 61% of patients (91/150) and BCF occurred in 51.3% (77/150). The Kaplan-Meier composite endpoint-free survival (CEFS) rate at 3 years was 40% (95% confidence interval [CI] 31-50) for the entire group. Kaplan-Meier estimates of CEFS were 100%, 49% and 24% at 3 years in the low-, intermediate- and high-risk groups pre-salvage HIFU, respectively. The Kaplan-Meier biochemical disease-free survival (BDFS) rate at 3 years was 48% (95% CI 39-59) for the entire group. Kaplan-Meier estimates of BDFS were 100%, 61% and 32% at 3 years in the low-, intermediate- and high-risk groups pre-salvage HIFU, respectively. Complications included urinary tract infection (11.3%; 17/150), bladder neck stricture (8%; 12/150), recto-urethral fistula after one HIFU procedure (2%; 3/150) and osteitis pubis (0.7%; 1/150).

Conclusion: Focal salvage HIFU conferred a relatively low complication and side effect rate. CEFS and biochemical control in the short to medium term were reasonable, especially in this relatively high-risk cohort, but still low compared with current whole-gland salvage therapies. Focal salvage therapy may offer disease control in men at high risk whilst minimizing additional treatment morbidities.