ESTRO 2025 - Abstract Book

S497

Clinical - Breast

ESTRO 2025

Conclusion: This phase II clinical trial demonstrates that S-PBI with Gamma-Pod is safe and associated with minimal toxicity for patients with early-stage breast cancer.

Keywords: partial breast irradiation, stereotactic,

1835

Digital Poster Metastasis-directed stereotactic radiotherapy and systemic treatment continuation for patients with oligoprogressive metastatic breast cancer Monica Milano 1 , Carmine Valenza 2,3 , Annamaria Ferrari 4 , Sara Gandini 5 , Dario Trapani 2,3 , Celeste Santoro 2,3 , Elena Battaiotto 2,3 , Ambra Carnevale Schianca 2,3 , Elisa Giordano 2,3 , Jalissa Katrini 2,3 , Maria Cristina Leonardi 4 , Samantha Dicuonzo 4 , Nadia Bianco 1 , Silvia Dellapasqua 1 , Elisabetta Munzone 1 , Giuseppe Curigliano 2,3 , Marco Colleoni 1 , Barbara Alicja Jereczek-Fossa 4,3 1 Division of Medical Senology, European Institute of Oncology, Milan, Italy. 2 Division of New Drugs and Early Drug Development for Innovative Therapies, European Institute of Oncology, Milan, Italy. 3 Department of Oncology and Hemato-Oncology, University of Milan, Milan, Italy. 4 Division of Radiation Oncology, European Institute of Oncology, Milan, Italy. 5 Department of Experimental Oncology, European Institute of Oncology, Milan, Italy Purpose/Objective: About 15-20% of patients with metastatic breast cancer (mBC) can experience oligoprogressive disease (OPD) in £5 sites of disease. Patients with OPD may benefit from metastasis-directed stereotactic radiotherapy (SBRT) to all sites of cancer progression, while maintaining the same systemic treatment, aiming to prolong the time to next systemic treatment (NEST). This study aims to assess the outcomes provided by this multimodal strategy. Material/Methods: Prospective-retrospective, single-center, cohort study including consecutive patients who received SBRT to all extracranial OPD sites (£5), from January 2011 to June 2023, without changing systemic therapy, according to the multidisciplinary tumor board's indication. The primary endpoint was post-radiotherapy progression-free survival (pRT-PFS). A sample size of 130 patients was needed to estimate a median pRT-PFS of 8 months with a 95% confidence interval (95%CI) ranging from 5.4 (considered clinically significant) to 10.6 months.