Evaluation of de novo oligometastatic prostate cancer patients managed with radiation therapy: A multi-institution, real-world dataset.

113 Background: Oligometastatic prostate cancer (omPCa) is an understudied entity, historically defined as ≤5 non-visceral metastases. However, its true prevalence in the molecular diagnostic imaging (MDI) era is unknown. Therapeutic clinical trials in advanced PCa based on conventional imaging modalities (CIM) complicate the ability to extrapolate findings to omPCa. Consequently, there is not a standard treatment approach; radiation therapy (RT) recommendations can vary widely. We sought to evaluate management and outcomes of de novo omPCa patients treated with RT in a multi-institutional cohort. Methods: Patients presenting with de novo omPCa (≤5 non-visceral lesions, allowance for >5 per physician discretion) diagnosed via CIM and/or MDI across 7 participating institutions were identified. Demographic/clinical data were collected. Clinical outcomes, including disease progression (any biochemical recurrence or distant failure) and survival were assessed. Progression-free survival (PFS) and overall survival (OS) were determined using the Kaplan-Meier method. Results: 163 patients treated with RT between 2015-2024 were analyzed (clinical data at diagnosis; Table). Over half of patients (90/163, 55%) were diagnosed using MDI, the remainder via CIM. 7% of patients presented with pelvic lymph nodes (LNs) only, 2% with non-regional LNs, 42% with bone only disease, and the remainder with a combination. Most patients (161/163) received systemic therapy. Of 131 patients with details, 39% received androgen deprivation therapy (ADT) alone, the remainder received ADT + androgen receptor signaling inhibitor (n=51); 8 also received docetaxel. 4% of patients received prostate RT alone, 5% of patients received prostate + pelvic RT, 17% of patients received metastasis-directed RT only, 36% of patients received prostate + pelvic + metastasis-directed RT, and 38.7% of patients received prostate + metastasis-directed RT. 152 patients had full follow-up (FU) details available. Median FU from time of omPCa diagnosis was 31 months (range, 3-229). Twenty-two patients developed distant metastases (outside of documented OM). Five-year OS from time of diagnosis was 91% (95%CI 80,97). Five-year PFS after RT was 51% (95%CI 30,68) with median PFS of 74 months (95%CI 41, not reached). Conclusions: In this contemporary real-world cohort, nearly all patients with de novo omPCa received systemic therapy and ~75% were treated with at least prostate + metastasis-directed RT. Identification of omPCa included both MDI and CIM, reflecting real-world patterns. Further analysis incorporating additional institutions, oligorecurrent and oligoprogressive patients is ongoing, and will evaluate the association of treatment characteristics on progression at last FU. Characteristic Age Gleason score PSA Number of lesions Median, range 68 (44-92) 8 (6-10) 17 (2-2670) 2 (1-8)