Real-world clinical outcomes of oligometastatic prostate cancer using SBRT: An Australian experience

Objectives

This work aimed to report real-world outcomes from the use of SBRT to treat ADT naïve, PSMA-detected oligometastatic prostate cancer (OPCa) and to assess disease and treatment characteristics in this heterogeneous population intersect or impact treatment response.

Subjects and Methods

This retrospective single-institution study examined PSMA-PET–detected oligometastases (n = 1–5) in ADT-naïve OPCa patients, treated with metastasis-directed therapy (MDT) using SBRT delivered via MRI- or CT-guided linear accelerator. Primary endpoint was biochemical progression free survival (PSA ≥ 25% if baseline <2 ng/mL or ≥2 ng/mL from nadir if baseline ≥ 2 ng/mL, start of systemic therapy, death). Secondary endpoints included time to PSA progression, time to next intervention, ADT-free survival. Univariate and multivariate analyses were conducted for prognostic factors associated with bPFS, time to PSA progression and PSA50 response. Baseline clinical and treatment characteristics, PSA responses and local failure rates were analysed. Those with castrate-resistant disease, prior systemic therapy or interval follow-up of <6 weeks were excluded.

Results

Sixty-seven patients treated from January 2019 to August 2024 were analysed with a median follow-up of 18.8 months. Ninety-three oligometastatic lesions were treated; 55.3% were treated for nodal disease, 38.8% bone and 5% with lung disease. All lesions were PSMA-detected with median SUVmax 6.3. Median bPFS was 22.1 m; TTNI was 28.8 m. Lower initial T stage and longer duration from OPCa diagnosis to MDT were associated with prolonged bPFS. Lower T stage and PSA doubling time >3 m at MDT were associated with prolonged time to PSA progression. Median PSA fall was 68.9%; PSA 50% response was observed in 55.2%. Twenty-nine patients (43%) had a complete metabolic response after MDT. Median ADT-free survival was not reached.

Conclusions

MDT in PSMA-PET-detected OPCa can provide clinically meaningful disease control in a subset of patients. This study supports this approach but warrants continued prospective study and exploration into the castrate-resistant setting.