S996
Clinical - Oligometastatic cancer
ESTRO 2026
cancer (HSPC) remains undefined. The biological behavior of M1a disease, whether it represents locoregional extension or early systemic spread, also remains uncertain in the era of treatment intensification. We evaluated survival outcomes of synchronous N1M0 and M1a HSPC treated with whole pelvic radiotherapy (WPRT) and elective nodal irradiation (ENI) to inform future prospective studies. Material/Methods: We retrospectively identified patients with synchronous N1M0 or M1a (limited to common iliac and/or retroperitoneal nodes) HSPC treated with consolidative radiotherapy including WPRT between 2016 and 2024. In patients with retroperitoneal involvement, the WPRT field could be extended up to the inferior margin of the kidney, along with any grossly involved nodes within the field. All patients received androgen deprivation therapy (ADT), with androgen receptor pathway inhibitors (ARPI) or chemotherapy added at the treating physician’s discretion. Patients with <18 months of follow-up were excluded. Biochemical recurrence was defined using the Phoenix criteria (nadir + 2 ng/mL). Primary outcomes included overall survival (OS), biochemical recurrence-free survival (bRFS), nodal recurrence-free survival (NRFS), and distant metastasis-free survival (DMFS), analyzed by Kaplan–Meier and log-rank tests. Multivariate analysis adjusting for systemic intensification is ongoing. Results: A total of 68 N1M0 and 39 M1a patients were included. ENI was delivered in 96 (89.7%), ARPI in 74 (69.2%), and chemotherapy in 5 (4.7%) patients. At a median follow-up of 39 months (IQR 27–58.5), 3-year OS was 92.6% for N1M0 and 90.0% for M1a; bRFS 91.7% vs. 81.6%; NRFS 95.5% vs. 84.2%; and DMFS 91.0% vs. 90.1%. At 5 years, OS was 92.6% vs. 84.7%; bRFS 81.5% vs. 76.5%; NRFS 82.3% vs. 68.1%; and DMFS 73.4% vs. 80.7% for N1M0 and M1a, respectively. There were no statistically significant differences between groups: OS (p = 0.6), bRFS (p = 0.4), NRFS (p = 0.06), and DMFS (p = 0.7).
Conclusion: SBRT provides excellent local control in
oligometastatic disease, confirming its effectiveness as a minimally invasive ablative treatment. A higher BED and non-colorectal tumours were associated with improved LC, whereas multiple lesions and repeat- induced recurrences predicted less favorable outcomes. Concomitant ST was independently associated with improved LC, supporting a potential synergistic effect between local and systemic treatments. Keywords: SBRT, LocalControl, Oligometastases Comparable survival in synchronous N1M0 and M1a hormone-sensitive prostate cancer after whole-pelvic radiotherapy and elective nodal irradiation Kayeong Shin 1 , Gregory Chronowski 1 , Marc E Delclos 1 , Comron J Hassanzadeh 1 , Sean E McGuire 1 , Henry Mok 1 , Chad Tang 1 , Steven J Frank 1 , Quynh-Nhu Nguyen 2 , Karen Hoffman 3 , Phuoc T Tran 1 , Paul Corn 4 , Brian F Chapin 5 , Devaki S Surashi 6 , Seungtaek Choi 1 1 GU Radiation oncology, The University of Texas, MD Anderson Cancer Center, Houston, USA. 2 Thoracic Radiation oncology, The University of Texas, MD Anderson Cancer Center, Houston, USA. 3 Breast Radiation oncology, The University of Texas, MD Anderson Cancer Center, Houston, USA. 4 GU Medical oncology, The University of Texas, MD Anderson Cancer Center, Houston, USA. 5 Urology, The University of Texas, MD Anderson Cancer Center, Houston, USA. 6 Nuclear Medicine, The University of Texas, MD Anderson Cancer Center, Houston, USA Digital Poster 5067
Purpose/Objective: The EXTEND trial demonstrated improved
progression-free survival with metastasis-directed therapy in metastatic prostate cancer, including both synchronous and metachronous onset. However, its effect in synchronous regional or non-regional node- positive (N1M0 or M1a) hormone-sensitive prostate
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