Systemic and tumor-directed therapy for oligometastatic prostate cancer (SOLAR): A phase II trial for veterans with de novo oligometastatic prostate cancer.

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163 Background: Treatment paradigms for oligometastatic castration-sensitive prostate cancer patients are evolving. Molecular imaging improves staging, intensified systemic and primary tumor directed therapy improves survival, metastasis-directed therapy improves local control. The impact of combining these imaging and therapeutic approaches into a planned multimodal treatment strategy is unknown. Here we report a prospective phase II single-arm trial combining local, metastasis-directed, and intensified systemic therapies of limited duration with the objective to durably render Veterans free of progression off therapy. Methods: Veterans with de novo M1a/b prostate cancer and 1-5 radiographically visible M1 lesions underwent radical local treatment, intensified systemic therapy for six months (leuprolide, abiraterone acetate with prednisone, apalutamide), and metastasis-directed stereotactic ablative radiotherapy (SBRT). Radical local therapy was either radical prostatectomy (n=12) with lymph node dissection and post-operative radiotherapy (pT≥3a, N1, or positive margins) or radical radiotherapy (n=12) directed to the prostate, SVs, and pelvic LNs. The primary endpoint was the percentage of patients achieving an undetectable serum PSA (for radical prostatectomy) or <2 ng/mL (for radical radiotherapy) six months after recovery of testosterone to ≥150 ng/dL. Secondary endpoints included time to biochemical progression, time to radiographic progression, time to initiation of alternative antineoplastic therapy, prostate cancer specific survival, health related quality-of-life, safety and tolerability. Results: Twenty-eight patients enrolled and 4 dropped out (3 prior to start of treatment). All were staged by PSMA PET/CT except two (one by Fluciclovine PET/CT, and one by NaF PET/CT, CT, MRI). Twenty-nine percent were M1a, seventy-one percent were M1b. Median follow-up was 30 months (range 20 - 61 months). Mean and median number of M1 metastases were both two. Sixty-two percent completed all planned systemic therapy without dose modification. One did not recover testosterone after 29 months. Twenty-two had >6 months follow-up after testosterone recovery, 19 of 22 (86%) remain free of any progression (primary endpoint). Three had metastatic progression, one poly nodal M1a progression, one multiple bone metastases, one multiple bone and nodal metastases. Grade 2 and 3 toxicities for primary tumor therapy were 46% and 4%; SBRT 0% and 0%; systemic therapy 42% and 4%. There was one Grade 4 toxicity. Conclusions: Although a small trial, a majority of patients with molecular imaging defined de novo oligometastatic prostate cancer treated with primary and metastasis-directed therapy with intensified systemic therapy of limited duration remained free of progression with a recovered testosterone off all active therapy. Clinical trial information: NCT03298087 .

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