Pooled Analysis of the SOLAR and SATURN Clinical Trials Comparing Progression of Synchronous Versus Metachronous Prostate-specific Membrane Antigen-defined Oligometastatic Prostate Cancer Following Systemic and Tumor-directed Therapy.

Juarez Casillas JE, Nikitas J, Rettig MB, Reiter RE, Lee A, Steinberg ML, Valle L, Kalbasi TR, Calais J, Czernin J, Eala MA, Tsai S, Kane N, Solanki AA, Sexton R, Duriseti S, Berenji GR, Aronson WJ, Garraway IP, Chang MG, Kwon R, Lee SP, Nickols NG, Kishan AU. Pooled Analysis of the SOLAR and SATURN Clinical Trials Comparing Progression of Synchronous Versus Metachronous Prostate-specific Membrane Antigen-defined Oligometastatic Prostate Cancer Following Systemic and Tumor-directed Therapy. European urology oncology. 2025 Jun 19 DOI: 10.1016/j.euo.2025.05.027.

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Abstract:

Multimodal strategies combining primary and metastasis-directed therapy (MDT) with short-term intensified systemic therapy may improve outcomes in oligometastatic castrate-sensitive prostate cancer (omCSPC) while minimizing long-term toxicity. This post hoc analysis of two prospective phase 2 trials, SOLAR (NCT03298087) and SATURN (NCT03902951), evaluated oncologic outcomes in prostate-specific membrane antigen positron emission tomography-defined synchronous and metachronous omCSPC ( 5 M1a-b lesions), respectively. All patients received 6 mo of intensified systemic therapy (leuprolide, abiraterone acetate with prednisone, and apalutamide) and stereotactic body radiotherapy to oligometastases. SOLAR patients were treatment-naïve and also underwent radical prostatectomy (RP) or definitive prostate-directed radiotherapy (dRT). SATURN enrolled patients with post-RP recurrences: among the 26 patients who completed protocol therapy, 12 (46%) had prior androgen deprivation therapy (ADT), six (23%) had prior MDT, and 17 (65%) had one to three prior recurrences. The primary endpoint for both studies was prostate-specific antigen (PSA) response, defined as < 0.05 ng/ml after RP or < 2 ng/ml after dRT at 6 mo after testosterone recovery ( 150 ng/dl). Secondary endpoints included progression-free survival (PFS) and eugonadal PFS starting from the time of testosterone recovery. Progression was determined biochemically using PSA thresholds of 0.05 ng/ml for post-RP and 2 ng/ml for post-dRT patients. Among 50 patients (24 synchronous and 26 metachronous), the synchronous omCSPC group had a significantly higher PSA response rate (83% vs 50%; p  =  0.018) and significantly longer PFS and eugonadal PFS (p  <  0.05). The metachronous subgroup with prior ADT had worse outcomes, suggesting increasing resistance with repeated systemic therapy.