Stereotactic body radiation therapy to postpone systemic therapy escalation for castration-resistant prostate cancer: A multicenter retrospective analysis.

Purpose: To evaluate the oncological outcome after stereotactic body radiation therapy (SBRT) for oligoprogressive metastatic castration-resistant prostate cancer (omCRPC) patients.

Materials-methods: In this retrospective, observational, multi-institutional study, omCRPC patients (≤5 metastases) underwent SBRT. Primary endpoint was systemic therapy escalation-free survival (STE-FS) after SBRT. Local relapse (LR), distant (DP) and isolated biochemical (iBP) progressions 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, 50 pts with omCRPC underwent SBRT. With a MFU of 23 months [3---100], median STE-FS was 13.1 months (95 %CI 10.8 - 36.4). Median OS was not reached and PFS was 13 months (CI95% 10.1 - 20.8). Post-SBRT PSA remained stable or decreased in 19 pts (38 %). Progression events (LR, DP, iBP) were observed in 34 pts (68 %), among whom 6 relapsed in the irradiated area (local control rate: 88 %). DP and iBP were observed in 28 pts (56 %) and 4 pts (8 %) respectively. In multivariate analysis, post-SBRT biochemical response was an independent prognostic factor for STE-FS. Grade ≥ 3 toxicity occurred in 2 pts.

Conclusion: With excellent local control and tolerance, SBRT for omCRPC patients represents an acceptable 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.