Systemic therapy escalation after stereotactic body radiation therapy for oligometastatic hormone-sensitive prostate cancer

PURPOSE: To evaluate the oncological outcome after stereotactic body radiation therapy (SBRT) for oligometastatic hormone-sensitive prostate cancer (omHSPC) patients. MATERIALS-METHODS: In this retrospective, observational, multi-institutional study, omHSPC patients (≤5 metastases) underwent SBRT. Primary endpoint was systemic therapy escalation-free survival (STE-FS) after SBRT. Local (LR), distant (DR), prostatic (PR) and isolated biochemical (iBR) relapses were reported with progression-free survival (PFS) and overall survival (OS). Prognostic factors for STE-FS were investigated. Toxicity was reported. RESULTS: From 01/07 to 09/19, 119 pts with omHSPC underwent SBRT. With a MFU of 34 months [12–97], median STE-FS was 33.4 months (95%CI 26.6–––40.1). Median OS was not reached and PFS was 22.7 months (CI95% 18.6–––32.3). Post-SBRT-PSA remained stable or decreased in 87 pts (73.1%). Progression events (LR, MR, PR, iBR) were observed in 72 pts (60.5%), among whom 6 relapsed in the irradiated area (local control rate: 95%). DR, BR, PR were observed in 44 pts (37%), 21pts (17.7%) and 2 pts (1.7%) respectively. In multivariate analysis, post-SBRT biochemical response was an independent prognostic factor for STE-FS. Grade ≥ 3 toxicity occurred in 1pt. CONCLUSION: With excellent local control and tolerance, SBRT for omHSPC patients represents an attractive approach to defer systemic therapeutic escalation and prevent its side effects. Accurate patient selection for SBRT requires more data with longer follow-up and higher numbers of patients pending the results of upcoming randomized trials.