ESTRO 2025 - Abstract Book

S611

Clinical - Breast

ESTRO 2025

4095

Digital Poster Impact of Stereotactic Body Radiotherapy (SBRT) on PFS and OS in Non-Bony Visceral Oligometastatic Breast Cancer: A Prospective Study ADHAR AMRITT 1 , Abhilash Dagar 1 , Adrija Ghosh 1 , Arjun Maity 1 , Jitendra Kumar Meena 2 , Akash Kumar 3 , Jyoti Sharma 4 , Jyoutishman Saikia 4 , Jaswin Raj 1 , Sangeeta Hazarika 1 , Aman Sharma 1 , Daya Nand Sharma 5 , Supriya Mallick 1 1 Radiation Oncology, NCI-AIIMS, New Delhi, India. 2 Preventive Oncology, NCI-AIIMS, New Delhi, India. 3 Medical Oncology, NCI-AIIMS, New Delhi, India. 4 Surgical Oncology, NCI-AIIMS, New Delhi, India. 5 Radiation Oncology, Dr BRA IRCH & NCI-AIIMS, New Delhi, India Purpose/Objective: Oligometastatic breast cancer (OMBC) is a subgroup resembling metastasis but behaving like locally-advanced disease. Stereotactic body radiotherapy (SBRT), combined with systemic therapy (ST), is increasingly used to improve progression-free survival (PFS), overall survival (OS), and delay the need for additional lines of ST 1 . Non bone visceral metastases (NBVM) have historically worse outcomes than bone metastases, and the optimal treatment approach remains unclear 2 . Material/Methods: A prospective study assessed the impact of metastatic-directed SBRT on PFS, OS, and local control in NBVM. Eligible patients, after baseline Whole Body PET-CT (WBPETCT) and exclusion of brain/bone metastasis, received SBRT and appropriate ST. Patients were pre-medicated with steroids before SBRT. Doses prescribed were: 45-50Gy/5# to liver, 54Gy/3# (peripheral lung), 60Gy/8# (central lung), 30Gy/3# to nodes, and 45Gy/3# to peritoneal deposits on Varian Trubeam LINAC. Response assessment at 3 months using RECIST v1.1. Pain score, GTV volume, PTV volume, and toxicity (RTOG) were documented. Chi-square and Spearman-correlation analyses were performed. All patients received standard NACT, surgery, and adjuvant therapy as indicated Results: Between December 2021 and October 2024, 28 patients with OMBC were recruited (median age 47 years, range 37 65), including 1 male (3.5%). Metastatic site distribution: liver (11), lung (7), nodes (6), other sites (4). Of 28, 15 patients were alive, 10 died, and 3 were lost to follow-up. Tumour subtypes: 35%TNBC, 28.5% Her2+, 2 Luminal-A, and 17% Luminal-B. Twenty were upfront metastatic, and 8 had progression after locoregional treatment. Eighteen patients underwent mastectomy post-NACT, while 6 were ineligible for surgery due to progression. The most common dose was 50Gy/5# (28%). Median GTV volume was 5.35cc and PTV volume was 14.35cc. Median PFS post SBRT was 8 months, and median OS was 33.5 months. SBRT site response: CR in 36%, PR in 25%, and PD in 8%. Distant progression occurred in 16%. The most common toxicity was Grade-2 pain flare in 10%. Liver metastasis had the lowest OS (15.05 months) compared to lung (26.9 months) and nodes (35.65 months) (p=0.031). The highest PFS was seen in liver metastases (10.3 months). Molecular subtypes, age, GTV/PTV volume, and site didn`t significantly impact PFS, OS, or systemic therapy change based on uni- and multivariate analysis, though trends suggested a negative correlation between GTV/PTV volume and OS in liver and lung metastases. Conclusion: SBRT to metastatic sites in OMBC patients leads to clinically meaningful survival benefits. This approach, combined with molecular subgrouping, may help select patients for tailored treatments

Keywords: SBRT, Oligometastatic, Non-bony visceral mets

References: 1. Palma DA, Olson R, Harrow S, Gaede S, Louie AV, Haasbeek C, Mulroy L, Lock M, Rodrigues GB, Yaremko BP, Schellenberg D, Ahmad B, Senthi S, Swaminath A, Kopek N, Liu M, Moore K, Currie S, Schlijper R, Bauman GS, Laba J, Qu XM, Warner A, Senan S. Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastatic