A Phase II Trial of Stereotactic Body Radiation Therapy and Androgen Deprivation for Oligometastases in Prostate Cancer (SBRT-SG 05)

Purpose: SBRT-Spanish Group-05 (ClinicalTrials.gov.Identifier: NCT02192788) is a collaborative (SBRT-SG, Grupo de Investigación Clínica en Oncología Radioterápica, and Sociedad Española de Oncología Radioterápica) prospective multicenter phase II trial testing stereotactic body radiation therapy (SBRT) and androgen deprivation therapy (ADT) in patients with oligorecurrent prostate cancer.

Methods and materials: Two cohorts of patients with prostate cancer in an oligorecurrent stage (hormone-sensitive in the principal cohort and castration-resistant in the exploratory cohort) were assigned to receive ADT and SBRT for at least 24 months from the time of the enrollment. Concomitant treatment with chemotherapy, abiraterone, or enzalutamide was not allowed. Oncologic outcomes were assessed in both cohorts. Toxicity was prospectively analyzed.

Results: From 2014 to 2019, 81 patients with a total of 126 lesions from 14 centers met the inclusion criteria, 14 of whom were castration-resistant. With a median follow-up of 40 months (12-58 months), 3-year local recurrence-free survival was 92.5% (95% CI, 79.9%-96.3%) and 85.7% (95% CI, 48.2%-95.6%) in the principal and exploratory cohorts, respectively. In the principal cohort, biochemical relapse-free survival and metastasis progression-free survival at 1, 2, and 3 years were 91% (95% CI, 81%-95.8%), 73.7% (95% CI, 61.1%-82.8%), 50.6% (95% CI, 36.2%-63.3%), and 92% (95% CI, 83%-97%), 81% (95% CI, 70%-89%), and 67% (95% CI, 53%-77%), respectively. In the exploratory cohort, metastasis progression-free survival at 1, 2, and 3 years was 64% (95% CI, 34%-83%), 43% (95% CI, 18%-66%), and 26% (95% CI, 7%-51%), respectively. None of the patients developed grade III or higher toxicity or symptoms related to local progression, and only 2 (2.4%) patients developed grade II toxicity.

Conclusions: The combination of SBRT and ADT is safe and shows favorable clinical outcomes in patients with hormone-sensitive and castration-resistant prostate cancer. Validation studies are needed in patients with castration-resistant prostate cancer.