Time to next systemic therapy after stereotactic body radiation therapy for oligoprogressive metastatic castrate-resistant prostate cancer.

Abstract

62 Background: Patients with castrate-resistant prostate cancer (CRPC) with progressive disease are generally require a change/escalation in systemic therapy. For patients with limited ( ≤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, but there is limited data describing this approach. Methods: This is a retrospective study of patients with oligoprogressive metastatic CRPC (omCRPC) treated with SBRT at a single center between 2011-2022. The primary endpoint was time to next systemic therapy (TTNST) after SBRT. Secondary endpoints included overall survival (OS) after SBRT and TTNST stratified by presence of untreated non-progressing metastases. Results: Thirty-two patients with omCRPC received SBRT to 38 metastases. Patients had a median age of 72.5 years (range 50.6-84.3) and median PSA 6.85 ng/mL (range 0.39-922.0) at time of SBRT. The majority had an ECOG of 1-2 (29 patients, 90.6%) and metastases detected on conventional CT and/or bone scans (26 patients, 81.3%). The most commonly utilized SBRT regimen was 3000 cGy in 5 fractions (18 metastases, 47.4%) (Table). Sixteen patients were treated to all known sites of disease, whereas 16 patients received SBRT to oligoprogressive metastases but had at least one untreated non-progressing metastasis at the time of SBRT. Of 32 patients, 23 (65.7%) received SBRT to bone only, 3 (9.4%) to lymph node (LN) only, and 6 (18.8%) to other sites (pelvic tumor, n=2; pelvic tumor + LN, n =1; LN + bone, n=1; dura + bone, n=1; liver, n=1). 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 median OS was 41.3 months. For patients with 0 versus ≥1 untreated non-progressing metastasis, TTNST was 11.3 versus 8.7 months, respectively (HR 0.67, 95% CI 0.33-1.36, logrank p=0.24). There were no grade ≥3 toxicities due to SBRT. Conclusions: In this cohort, patients with omCRPC treated with SBRT delayed the next line of systemic therapy for a median of 10.1 months. SBRT in patients with omCRPC may delay initiation of next line systemic therapy in well selected patients, including those with ≥1 untreated non-progressing metastases. [Table: see text]