ESTRO 2025 - Abstract Book

S531

Clinical - Breast

ESTRO 2025

Figure.2 Conclusion:

With modest pCR rates, extreme hypofractionation (including SBRT) provides logistical advantages with reduced morbidity compared to sequential chemo-radiotherapy. However, further trials are necessary to test other potential advantages.

Keywords: Preoperative RT, Hypofractionation

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Poster Discussion IBISCO phase II trial: preoperative SBRT boost associated with neoadjuvant chemotherapy in Luminal B breast cancer (NCT05673304) Alice Zamagni 1,2 , Letizia Cavallini 3,2 , Giorgio Coco 2 , Gianfranco Cicoria 4 , Arina A Zamfir 2 , Antonio De Leo 5,6 , Francesca Abbati 7 , Angelo G Corradini 6 , Lidia Strigari 4 , Alessio G Morganti 5,2 1 Radioterapia Oncologica, Azienda USL – IRCCS di Reggio Emilia, Reggio Emilia, Italy. 2 Radiation Oncology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy. 3 Radiation Oncology Unit, Santa Maria della Misericordia Hospital, ULSS 5, Rovigo, Italy. 4 Department of Medical Physics, IRCCS Azienda Ospedaliero Universitaria di Bologna, Bologna, Italy. 5 Department of Medical and Surgical Sciences-DIMEC, Alma Mater Studiorum University of Bologna, Bologna, Italy. 6 Department of Pathology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy. 7 Addarii Medical Oncology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy Purpose/Objective: Pathological complete response (pCR) following neoadjuvant systemic therapy is a key predictor of disease outcomes and survival in aggressive breast cancer (BC) subtypes, particularly in triple-negative and Her2-positive BC. However, achieving pCR in Luminal B BC remains challenging, highlighting the need for innovative treatment strategies. The IBISCO trial explores the efficacy of combining preoperative stereotactic radiotherapy (SBRT) boost with standard neoadjuvant chemotherapy (NAC) to improve pCR rates in this context. Material/Methods: IBISCO, a phase II trial, aims to increase pCR rates from 15% to 35% in Luminal B BC patients by integrating a preoperative SBRT boost with standard NAC (weekly paclitaxel for 12 weeks, followed by Epirubicine-Ciclofosfamide for 4 cycles). The primary endpoint is assessed using the Residual Cancer Burden index. Additionally, exploratory analyses include evaluating changes in the tumor-associated inflammatory microenvironment and tumor genomic profile post-SBRT. Standard clinical practice will guide surgery and adjuvant therapies post-neoadjuvant treatment.