Phase II Trial of SBRT and Hormone Therapy for Oligometastases in Prostate Cancer

Abstract

SBRT-SG 05 (ClinicalTrials.gov Identifier: NCT02192788) is a collaborative (SBRT-SG, GICOR and SEOR) prospective multicenter phase II trial testing SBRT and hormone therapy (HT) in oligometastatic prostate cancer patients. The hypothesis is that SBRT can control the macroscopic disease and HT the microscopic one, as well as to test in hormone-sensitive (HS) patients the pause of the HT after biochemical control is achieved and that Castration Resistant prostate cancer (CRPC) is not radioresistant prostate cancer, and SBRT can delay new systemic treatments. Prostate cancer patients (HS or CRPC) in an oligorecurrent stage defined as less than 5 bone or lymph node metastases (including spinal bones) by Choline PET-CT or/and WB-DWI-MRI after primary treatment, were assigned to receive SBRT: Vertebral metastases: 1x16-18Gy or 3x8-9Gy; lymph node metastases: 3x10-11 Gy or 6x7,5Gy; non-spinal bone metastases: 1x16Gy or 3x10Gy. Inclusion criteria included: time from primary treatment to biochemical recurrence > 1 year and PSA doubling time> 2 months. A minimum of 24 months of LhRh analogues from the time of the enrollment was required. In HS patients, its withdrawal can be considered after two years of treatment if biochemical control is achieved. Local control rates, biochemical control rates and progression free survival were assessed. Toxicity was prospectively evaluated according to CTCAE.4 criteria. Previous or concomitant treatment with chemotherapy, abiraterone or enzalutamide was not allowed. From 07/2014 to 12/2018, 81 patients from 14 Spanish centers were recruited with a total of 117 oligometastases treated, 67 in lymph nodes, 43 in non-spinal bones and 7 in spinal bones. Fourteen patients had CRPC. With a median follow-up after SBRT of 22 months, (range 4,2–48,9 months) local control was 100% and biochemical control was 97,5%. Median Progression free survival was 36,4 months (IC95%= 32,3 – 40,5). 14 patients (17,3%) presented distant disease progression, 4 of them were CRPC. Seven of those 14 patients who relapsed were treated again with SBRT at that time. Specifically, in patients with CRPC, with a median follow-up after SBRT of 24,1 months (range 4,2 -48,9), the median PFS was 26,3 months, (range 17,3–35,3 months). 10 of the 14 CRPC patients (71%) are free from disease progression at last follow-up without the need to start second generation hormonal treatment or chemotherapy. Tolerance and toxicity profiles were excellent, none of the patients developed toxicity ≥G3 or symptoms related to local progression of the disease. These results indicate that the combination of SBRT and HT is a safe treatment approach with encouraging local and biochemical control in hormone-sensitive and in castration-resistant prostate cancer.