Predictors of Relapse in Oligometastatic Prostate Patients Receiving Stereotactic Ablative Radiotherapy.

Abstract

ObjectivesTo identify predictors of relapse in oligometastatic prostate cancer patients treated with Stereotactic Ablative Radiotherapy (SABR).MethodsThis retrospective study included 57 patients with metachronous oligometastatic prostate cancer treated with SABR between January 2018 and December 2023. SABR was delivered with a median dose of 30 Gy (range 24-36 Gy) in 3-5 fractions. The primary endpoint was disease-free survival, while secondary endpoints included local relapse rates. Kaplan-Meier survival estimation and Cox proportional hazards regression analyses were used to identify prognostic factors.ResultsWith a median follow-up of 34.5 months, the 1-year and 2-year DFS rates were 64.5% and 24.3%, respectively. Local control was achieved in 87% of patients. Multivariate analysis revealed post-SABR PSA reduction as the only significant predictor of relapse (HR = 0.235, 95% CI: 0.085-0.644, p = 0.005), indicating a 76.5% lower risk of recurrence in patients demonstrating substantial PSA declines after treatment. Traditional prognostic markers, including Gleason score, initial PSA levels, prior hormone therapy, and metastatic site did not significantly correlate with relapse risk.ConclusionsPost-SABR PSA kinetics are a more reliable predictor of relapse than conventional risk stratification factors in oligometastatic prostate cancer patients.Advances in knowledgeIn this single-centre cohort of metachronous oligometastatic prostate cancer treated with SABR (including both nodal and osseous metastases), early post-SABR PSA reduction was independently associated with relapse risk. These findings provide additional quantitative support for PSA dynamics as a pragmatic biomarker that may help stratify follow-up intensity and identify patients at higher likelihood of occult systemic disease, warranting prospective validation.