Time to Next Systemic Therapy After Stereotactic Body Radiation Therapy for Oligoprogressive Metastatic Castrate-Resistant Prostate Cancer.

Abstract

Purpose: Patients with metastatic castrate-resistant prostate cancer (CRPC) with progressive disease generally require a change or escalation in systemic therapy. For patients with limited (1-3) sites of progressive disease (oligoprogression), metastasis-directed therapy with stereotactic body radiation therapy (SBRT) may allow a longer interval before next-line systemic therapy.

Methods and materials: This is a retrospective study of patients with oligoprogressive metastatic CRPC (mCRPC) treated with SBRT at a single center between 2011 and 2022. The primary endpoint was time to next systemic therapy (TTNST) after SBRT stratified by the presence/absence of untreated nonprogressing metastases. Secondary endpoints included TTNST of the overall cohort and median overall survival (OS) after SBRT.

Results: Thirty-two patients with oligoprogressive mCRPC received SBRT to 38 metastases. Patients had a median age of 72.5 years (range, 50.6-84.3) and a median PSA of 6.85 ng/mL (range, 0.39-922.0) at the time of SBRT. The most commonly used SBRT regimen was 3000 cGy in 5 fractions (18 metastases, 47.4%). Sixteen patients were treated to all known sites of disease, whereas 16 patients received SBRT to oligoprogressive metastases but had at least 1 untreated nonprogressing metastasis at the time of SBRT. Patients had received a median of 1.0 prior line of androgen receptor signaling inhibitors and were predominantly (26 patients, 81.3%) chemotherapy naïve. Following SBRT, the median TTNST was 10.1 months and the median OS was 41.3 months. For patients with 0 versus ≥1 untreated nonprogressing metastasis, TTNST was 11.3 versus 8.7 months, respectively (HR, 0.67; 95% CI, 0.33-1.36, logrank P = .24). There was no grade ≥3 toxicities because of SBRT.

Conclusions: In this cohort, patients with oligoprogressive mCRPC treated with SBRT delayed the next line of systemic therapy for a median of 10.1 months. SBRT in patients with oligoprogressive mCRPC may delay initiation of the next-line systemic therapy in well-selected patients, including those with ≥1 untreated nonprogressing metastasis.