Phase II trial of image-guided oligometastatectomy and radiation therapy in recurrent prostate cancer (SOAR).

38 Background: In a subset of patients with molecular-imaging defined recurrent oligometastatic prostate cancer (PCa), salvage oligometastatectomy with surgery and/or radiation may provide improved androgen deprivation therapy (ADT)-free survival. Methods: This is a phase II trial with oligorecurrent PCa after primary prostatectomy or radiation therapy detected on Axumin (n=11) or Prostate-Specific Membrane Antigen (PSMA) (n=9) positron emission tomography. Oligometastatic disease was defined as ≤ 10 total sites, either of lymph node (LN) only (Group A), bone only (Group B), or LN and bone (Group C). Surgical intervention for patients with LN disease included extended pelvic and/or retroperitoneal LN dissection, depending on the location of the LNs. Groups A and C received adjuvant IMRT without ADT if PSA response was ≥ 1/3 decrease but remained ≥ 0.2 ng/dL. The primary outcome was a reduction in PSA by ≥ 50% at 6 months. Secondary objectives included PSA progression free-survival (PSA-PFS), ADT-free survival, and safety. Results: We accrued a total of 20 patients. The median age was 65 years (IQR 61-70), 95% (19/20) had an ECOG of 0, and 10% (2/20) were Hispanic. All patients had a prior prostatectomy, after which 45% (9/20) received adjuvant/salvage RT, with 33% (3/9) including the pelvis/ prostate bed. 30% (6/20) had exposure to ADT before trial treatment. The median time from definitive prostate cancer treatment to trial treatment was 2.8 years (IQR: 0.9-6.0). Oligorecurrent disease occurred as lymph nodes only (18/20; 90%) or bony (2/20; 10%). Within Group A, one patient completed adjuvant RT. The average number of imaging-identified positive LNs was 1.8 (range 1-6). The primary endpoint of reduction in PSA by ≥ 50% at 6 months was 40% (95%CI 19-64%) (Table 1). The secondary endpoint of PSA-PFS at 12 months was 84.4% (95%CI 66.6-100%). ADT-free survival at 12-months was 71.4% (95% CI 52.7% - 96.6%). There were no Clavien Grade III-IV complications. Conclusions: Salvage treatment of oligometastatic disease after prostatectomy or radiation identified on molecular imaging is feasible and safe. Nearly half the cohort had a good response to salvage treatment, demonstrated by a ≥ 50% reduction in PSA at 6 months. Ongoing analyses include comparing imaging and pathology correlations, and comparing complete/ partial responders and treatment failure. Further research is needed to identify ideal candidates for salvage treatment. Clinical trial information: NCT03796767 . PSA progression-free survival at 6- and 12-months (PFS). Time Estimate 95% Confidence Interval 6 months 100% --- 12 months 84.4% 66.6-100%