The role of stereotactic body radiotherapy in oligoprogressive prostate cancer: A site-specific analysis of the prospective, phase II RADIANT trial.

[BACKGROUND AND PURPOSE] Changing to next-line systemic therapy is the standard-of-care for patients with progressive metastatic castrate-resistant prostate cancer. However, to preserve systemic therapy options and minimize toxicity, stereotactic body radiation therapy (SBRT) is being increasingly considered for patients with limited disease progression ('oligoprogression'). Herein, we report clinical, toxicity and quality of life (QOL) outcomes for an oligoprogressive prostate cancer cohort from a prospective trial.

[MATERIALS AND METHODS] RADIANT (NCT04122469) was a single-arm, phase-II basket trial which included patients with metastatic prostate cancer on any systemic therapy ≥ 3 months, with radiographic evidence of oligoprogression in ≤ 5 sites. Analysis by disease site was planned a priori. Patients received SBRT in 1-5 fractions to all progressive sites and were maintained on their current systemic therapy. The primary endpoint was cumulative incidence of change in systemic therapy. Key secondary endpoints included local control, toxicity and health-related (HR) QOL.

[RESULTS] Thirty-two patients were analyzed; median age was 74.0 years, median PSA 6.7 µg/L, 25% with visceral metastases and a median of 2 prior systemic therapy lines. Median follow-up was 14.1 months (range 4.8-51.9 months). At 1-year, 55.1% of patients remained on the same systemic line and local control was 84.0%. The cumulative incidence of grade 2 toxicity was 25.0% at 1 year, with no grade 3+ toxicities. HRQOL was maintained, with no detriment following SBRT delivery.

[CONCLUSION] Among patients with oligoprogressive prostate cancer, SBRT is an effective and safe intervention, including in patients with aggressive clinicopathologic features. Larger, randomized trials are needed to validate these findings.