S1225
Clinical - Urology
ESTRO 2026
Results: The median follow-up was 51.4 months (3.6–198.4). 5- year Overall Survival was 75%.Biochemical recurrence occurred in 194 cases (61%), with a median PSA doubling time of 1.31 months.Local Recurrence occurred in 20 cases (6%), with a 5-year Local Recurrence-Free Survival (LRFS) of 93%. Regional recurrence was observed in 28 cases (9%), with a 5- year Regional Relapse-Free Survival of 89%.Among the 116 concomitantly treatments performed to the prostate or prostate bed, local recurrence was detected in 3 cases. 5-year Distant Metastasis-Free Survival was 58%.Distant metastases occurred in 132 cases (41.6%).No pts experienced acute toxicity of grade(G) ≥ 3 and only two cases of late G3 genitourinary toxicity were reported (both in the ENRT group in pts treated to the prostate bed). Conclusion: Salvage ENRT/SBRT for nodal relapse is effective with 93 % 5 year-LRFS and low toxicities.Prospective randomized studies with long follow-up are required to choose the best approach. Keywords: MDT, prostate cance, EBRT, SBRT Poster Discussion 2331 Predictive value of the circulating T-cell receptor repertoire in oligorecurrent prostate cancer treated with SBRT: results from a prospective trial Fabio Matrone 1 , Elena Muraro 2 , Matteo Turetta 2 , Marcella Montico 3 , Agostino Steffan 2 , Francesca Gessoni 1 , Lucia Fratino 4 , Alessandra Donofrio 1 , Veronica Paduano 5 , Raja Dhibi 2 , Martina Zanchetta 3 , Fabio Del Ben 2 , Giulia Brisotto 2 1 Department of Radiation Oncology, 1Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Aviano, Italy. 2 Immunopathology and Cancer Biomarkers Units, Department of Cancer Research and Advanced Diagnostics, 1Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Aviano, Italy. 3 Clinical Trial Office, Scientific Direction, 1Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Aviano, Italy. 4 Department of Medical Oncology, 1Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Aviano, Italy. 5 CRO Biobank, 1Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, Aviano, Italy Purpose/Objective: Stereotactic Body Radiotherapy (SBRT) is increasingly employed as metastasis-directed therapy for oligorecurrent hormone-sensitive prostate cancer (orHSPC). However, patient outcomes remain heterogeneous, underscoring the need for reliable biomarkers to identify individuals at higher risk of systemic progression. SBRT has been shown to modulate immune responses, including T-cell receptor
(TCR) diversity [1-2]. This study aimed to characterize longitudinal changes in the circulating TCR repertoire before and after SBRT and to assess their potential predictive value for distant metastasis control. Material/Methods: A prospective cohort of 34 orHSPC patients with 1–3 nodal and/or bone metastases was enrolled and treated with SBRT. The median follow-up was 42.1 months. Peripheral blood samples were obtained at baseline (T0), and at 1 (T1) and 3 months (T2) post- SBRT. Genomic DNA was extracted from buffy coat (n = 102 samples) and analyzed by multiplex PCR and deep sequencing of the TCR β CDR3 region using the ImmunoSEQ® platform (Adaptive Biotechnologies). TCR repertoire was evaluated through richness (Chao index), diversity (Shannon index), and clonality (Gini coefficient). The clinical endpoint was Distant Progression-Free Survival (DPFS), defined as the time from SBRT to the development of new distant metastases. Results: Across the entire cohort, a significant increase in TCR richness was detected following SBRT, both from T0 to T2 and from T1 to T2 (p ≤ 0.01) (Figure 1). No significant changes were observed in overall diversity or clonality across the three time points. When stratified by clinical outcome, patients maintaining higher post-treatment TCR richness and diversity achieved significantly longer 2-year DPFS compared with those who experienced distant progression (p ≤ 0.01). Conversely, an increase in TCR clonality after SBRT was associated with poorer prognosis (p ≤ 0.05) (Figure 2).
Conclusion: SBRT in orHSPC induces a measurable expansion of circulating TCR richness, potentially reflecting systemic T-cell activation. Variations in post-treatment diversity and clonality correlate with metastatic progression risk, suggesting that TCR repertoire profiling may serve as a minimally invasive biomarker for outcome prediction after SBRT. Further validation in larger,
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