Predictors of Long-Term Disease-Free Survival With Stereotactic Body Radiation Therapy for Oligometastatic Prostate Cancer

Abstract

Purpose: Stereotactic body radiation therapy (SBRT) is increasingly used for oligometastatic prostate cancer, although most published series include mixed histologies and only a few patients achieve long-term disease-free survival. This retrospective study presents one of the largest prostate-only cohorts, aiming to identify who benefits most from SBRT.

Methods and materials: From 2011 to 2023, 234 patients with ≤3 hormone-sensitive metachronous prostate cancer oligometastases were treated with SBRT at the Royal Marsden Hospital, London, and Sutton, UK. Concurrent androgen deprivation therapy (ADT) was allowed by clinician discretion. Treatment and outcome data were collected to assess the association between covariates and radiological progression-free survival (rPFS), ADT-free survival, and prostate cancer-specific survival (PCSS).

Results: In total, 308 lesions were treated in 234 patients. After a median follow-up of 56.5 months, median rPFS was 22 months and ADT-free survival was 42 months. The 5-year rPFS, ADT-free survival, and PCSS were 22.9%, 42.3%, and 96.4%, respectively. Concurrent ADT was used in 140 patients (59.8%). Prostate-specific antigen doubling time ≤ 3 months was a significant predictor for shorter rPFS [hazard ratio (95% CI) 1.52 (1.07-2.16), P = .001], and concurrent ADT use improved rPFS [0.52 (0.37-0.73), P < .001]. Nodal disease at primary presentation [2.08 (1.10-3.92), P = .023] and greater than 1 oligometastases [1.88 (1.25-2.82), P = .002] were inversely associated with ADT-free survival. Concurrent ADT use [0.40 (0.27-0.58), P < .001] improved ADT-free survival. Concurrent ADT use with SBRT did not improve eugonadal rPFS and eugonadal ADT-free survival. Patients diagnosed with oligometastases using baseline prostate-specific membrane antigen positron emission tomography/computed tomography had longer median ADT-free survival than those diagnosed with "other" imaging methods (52 vs 32 months, P = .041). For PCSS, more than 1 oligometastasis [6.08 (1.20-30.78), P = .029] and nodal disease at primary presentation [6.48 (1.16-36.15), P = .033] were associated with worse survival [5.95 (1.02-34.9), P = .048].

Conclusions: We present one of the largest SBRT case series specific to hormone-sensitive metachronous oligometastatic prostate cancer. After 5 years, 22.9% remained radiologically recurrence free and 42.3% remained ADT-free.