Purpose: The aim of the present study was to provide predictive factors for survival outcomes of oligometastatic prostate cancer (PC) patients treated with stereotactic body radiation therapy (SBRT) as a metastases-directed therapy (MDT).
Methods: In this cohort study, endpoints included overall survival (OS), progression-free survival (PFS), distant progression-free survival (DFS) and local control of treated metastases (LC). The binary classification tree approach with recursive partitioning analysis (RPA) was applied to stratify the patients into risk groups based on OS, PFS and DPFS; for each endpoint, disease-free interval (DFI) was calculated. We included patients with synchronous or metachronous metastases from prostate adenocarcinoma treated with SBRT.
Results: 119 Metastases were treated with SBRT in 92 patients. Median follow-up was 22.2 months. Rates of OS at 1 and 3 years were 96.9% and 88.0%, while DPFS was 51.9% and 20.9%. Recursive partitioning analysis identified three prognostic classes for OS: Class 1: castration-sensitive patients (3 years OS 95%); Class 2: castration-resistant patients with low-intermediate risk NCCN disease (3 years OS 88.8%); Class 3: castration-resistant patients with high-risk NCCN disease (3 years OS 76.9%). Regarding DPFS, RPA divided patients into two classes, according to a cutoff value of DFI of 34 months (3 years PFS of 28.7% vs 5.8%). Three classes were identified for DPFS: Class 1: DFI < 34 months (3 years DPFS 9.1%); Class 2: DFI > 34 months and high-risk NCCN PC (3 years DPFS 21%); Class 3: DFI > 34 months and low-intermediate risk NCCN disease (3 years DPFS 60.2%).
Conclusion: Oligometastatic PC represents nowadays a setting of particular interest in which local ablative therapies play a decisive role. In the present study, we recognized the importance of DFI, together with NCCN class risk, to predict the risk of new metastases after SBRT in oligometastatic PC.
Keywords: Oligometastases; Oligometastatic; PSA kinetics; Prostate cancer; Radiotherapy; SBRT; Stereotactic body radiation therapy.