BACKGROUND: The role of metastasis-directed therapy (MDT) in castration-resistant prostate cancer (CRPC) remains unclear. Prostate Cancer Study 9 (PCS-9) aimed to evaluate the benefits of stereotactic body radiotherapy (SBRT) in addition to standard systemic therapy in patients with oligometastatic CRPC.
METHODS: This open-label, randomised, phase 2 trial was conducted across 13 Canadian academic and community oncology centres. Male patients aged 18 years or older, with an Eastern Cooperative Oncology Group performance status of 0-2, and histologically confirmed oligometastatic CRPC (≤5 metastases), who had progressed on androgen deprivation therapy (ADT), were randomly assigned (1:1) to ADT-enzalutamide (ENZA; 160 mg once daily) or ADT-ENZA-SBRT to all oligometastatic sites. Randomisation was completed by sequentially numbered, sealed opaque envelopes, and stratified by the location of the metastasis. The primary endpoint was radiographic progression-free survival. Analysis was performed on an intention-to-treat basis. This study is registered with ClinicalTrials.gov, NCT02685397, and was halted and completed at the phase 2 stage.
FINDINGS: Between Oct 18, 2016, and July 31, 2023, 102 male patients were randomly assigned to ADT-ENZA (n=49) or ADT-ENZA-SBRT (n=53); after excluding one patient per treatment group due to early withdrawal and insufficient data, 48 patients in the ADT-ENZA group and 52 patients in the ADT-ENZA-SBRT group were included in the final analysis. Most patients were White (80 [80%]) and median age was 73·0 years (IQR 67·0-79·5). At a median follow-up of 4·8 years (IQR 3·4-5·0), ADT-ENZA-SBRT significantly improved radiographic progression-free survival compared with ADT-ENZA alone (median radiographic progression-free survival, 4·6 years [95% CI 3·7-not reached] vs 2·3 years [1·4-3·7]; hazard ratio 0·48 [95% CI 0·27-0·86]; p=0·014). The most common grade 3 treatment related adverse event was impotence (eight [57%] of 14 patients in the ADT-ENZA group and nine [75%] of 12 patients in the ADT-ENZA-SBRT group). There were no grade 4 toxicities and no treatment-related deaths.
INTERPRETATION: These results demonstrate that SBRT, when combined with ADT-ENZA, prolongs disease control in oligometastatic CRPC by doubling median radiographic progression-free survival, with similar toxicity profiles between the groups. These findings support integrating SBRT into the treatment paradigm for oligometastatic CRPC.
FUNDING: Jewish General Hospital (Astellas Canada).