S1243
Clinical - Urology
ESTRO 2026
Croatia. 9 Clinic for oncology, UHC Split, Split, Croatia. 10 School of medicine, University of Split, Split, Croatia. 11 School of medicine, University of Rijeka, Rijeka, Croatia. 12 School of dental medicine, University of Zagreb, Zagreb, Croatia Purpose/Objective: Immunotherapy is standard treatment for metastatic renal cell carcinoma (mRCC) and combination with stereotactic body radiotherapy (SBRT) offers a promising local treatment for (oligo)progressive disease. This study aim to evaluate oncological outcomes of mRCC patients treated with immunotherapy and explore the impact of SBRT on disease control. Material/Methods: We retrospectively collected data on mRCC patients treated with immunotherapy at three Croatian oncology centers from 2019 to 2025. Variables included clinical characteristics, International Metastatic RCC Database Consortium (IMDC) risk group, metastatic burden, systemic therapy details, SBRT parameters, radiological response, and timing relative to immunotherapy. Primary endpoints were progression-free survival (PFS) and overall survival (OS). Univariate and multivariate analyses assessed associations between clinical factors (age, sex, ECOG, brain metastases, nephrectomy, treatment line, baseline neutrophil-to-lymphocyte ratio [NLR], metastatic extent, SBRT use, IMDC group) and clinical outcomes. Results: In 71 analized patients, 48% received first-line immunotherapy (ipilimumab/nivolumab or nivolumab monotherapy) and 52% second-line nivolumab after tyrosine kinase inhibitor (TKI) failure. Twenty-seven patients (38%) underwent additional SBRT for (oligo)progression. Baseline characteristics: median age 64 years, 76% male, 86% nephrectomized, 72% polymetastatic (>5 metastases), 9% brain metastases, 85% clear cell histology, 32% ECOG ≥ 1. IMDC risk distribution: 11% favorable, 64% intermediate, 24% poor. Median SBRT-treated lesions per patient were 2 (range 1–14); median biologically effective dose (BED7) was 100 Gy (range 51–140 Gy). Median follow-up was 39 months. Disease progression occurred in 54%, and 56% of the patients died. Six-month local control of SBRT-treated lesions was 95%. Median PFS and OS were 17 and 27 months, respectively. SBRT was the only factor significantly associated with improved PFS (HR 0.4, p=0.003) (Figure 1., PFS probability regarding SBRT). For OS, ECOG, NLR, cytoreductive nephrectomy, and SBRT were significant on univariate analysis; on multivariate analysis, NLR (HR 1.2, p=0.02) and SBRT (HR 0.4, p=0.04) remained significant (Figure 2., OS probability regarding SBRT). Nineteen percent of patients treated with SBRT continue on
combination persisted beyond pharmacologic castration.The Sankey visualization (Figure 2) demonstrated distinct post-recovery trajectories: most Arm B patients remained metastasis-free, whereas Arm A patients more frequently transitioned to new
metastases. Conclusion:
In the RADIOSA trial, both MFS and eugonadal MFS favored SBRT + short-term ADT, with a persistent and statistically significant benefit after testosterone recovery.These findings support MFS as an adaptable surrogate endpoint for long-term disease control and treatment intensification strategies in oligorecurrent prostate cancer. The sustained eugonadal benefit reinforces the concept of a durable biological synergy between local ablation and transient androgen suppression, extending beyond on-treatment effects. References: 1. Marvaso G, Corrao G, Zaffaroni M, Vincini MG, Lorubbio C, Gandini S, Fodor C, Netti S, Zerini D, Luzzago S, Mistretta FA, Venetis K, Cursano G, Burla T, Mazzocco K, Cattani F, Petralia G, Fusco N, Pravettoni G, Musi G, De Cobelli O, Tang C, Ost P, Palma DA, Orecchia R, Jereczek-Fossa BA. ADT with SBRT versus SBRT alone for hormone-sensitive oligorecurrent prostate cancer (RADIOSA): a randomised, open-label, phase 2 clinical trial. Lancet Oncol. 2025 Mar;26(3):300- 311. doi: 10.1016/S1470-2045(24)00730-7. PMID: 40049196.CopyDownload .nbibFormat: Keywords: RADIOSa, SBRT, Oligometastatic, prostate cancer Digital Poster Highlight 2869 Synergistic Use of Stereotactic Body Radiotherapy and Immunotherapy in Advanced Renal Cell Carcinoma: Croatian Uro-Oncology Network Experience Hrvoje Br č i ć 1 , Matea Leki ć 2 , Klara Br č i ć 3 , Angela Prgomet Se č an 1 , Jure Murgi ć 1,4 , Marijana Jazvi ć 1 , Igor Toma š kovi ć 5,6 , Pero Bokarica 7 , Hrvoje Kau č i ć 2,6 , Mladen Solari ć 2 , Hrvoje Š obat 2 , Mirela Š ambi ć Penc 8 , Tomislav Omr č en 9,10 , Dragan Schwarz 2,11 , Ana Fröbe 1,12 1 Clinic for oncology and nuclear medicine, Sestre milosrdnice UHC, Zagreb, Croatia. 2 Clinic for radiosurgery and radiotherapy, Special Hospital Radiochirurgia Zagreb, Sveta Nedjelja, Croatia. 3 Department of haematology, Sestre milosrdnice UHC, Zagreb, Croatia. 4 School of medicine, Croatian Catholic University of Zagreb, Zagreb, Croatia. 5 Clinic for urology, Sestre milosrdnice UHC, Zagreb, Croatia. 6 School of medicine, Josip Juraj Strossmayer University of Osijek, Osijek, Croatia. 7 Department for urology, Clinical Hospital Sveti Duh, Zagreb, Croatia. 8 Clinic for radiotherapy and oncology, UHC Osijek, Osijek,
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