ESTRO 2024 - Abstract Book

S732

Clinical - Breast

ESTRO 2024

et al

1 University Hospital of Modena, Department of Radiation Oncology, Modena, Italy. 2 Bellaria Hospital — AUSL Bologna, Department of Radiation Oncology, Bologna, Italy. 3 Azienda USL-IRCCS di Reggio Emilia, Department of Radiation Oncology, Reggio Emilia, Italy. 4 Instituut Verbeeten, Department of Radiation Oncology, Tilburg, Netherlands. 5 Radiotherapiegroep, Department of Radiation Oncology, Arnhem/Ede, Netherlands. 6 Casa Sollievo della Sofferenza, Department of Radiation Oncology, San Giovanni Rotondo, Italy. 7 Maastricht University Medical Centre1 — GROW School for Oncology and Reproduction, Department of Radiation Oncology, Maastricht, Netherlands. 8 Medisch Spectrum Twente, Department of Radiation Oncology, Enschede, Netherlands. 9 IOSI (Oncology Institute of Italian Switzerland), Department of Radiation Oncology, Bellinzona, Switzerland. 10 Presidio Ospedaliero S.Anna — ASST Lariana, Department of Radiation Oncology, Como, Italy. 11 University of Groningen — University Medical Center Groningen, Department of Radiation Oncology, Groningen, Netherlands. 12 University Hospital of Modena, Department of Methodological and Statistical Support for Clinical Research, Modena, Italy. 13 University of Modena and Reggio Emilia, Department of Medical and Surgical Sciences, Modena, Italy. 14 Iridium Netwerk, Department of Radiation Oncology, Wilrijk-Antwerp, Belgium. 15 University of Antwerp, Faculty of Medicine and Health Sciences, Wilrijk-Antwerp, Belgium

Purpose/Objective:

Several randomized phase 3 trials have investigated the value of accelerated partial breast irradiation (APBI) for patients with early breast cancer after breast-conserving surgery compared with whole-breast irradiation (WBI). Here we report primary endpoint results for all patients enrolled in the IRMA trial (ClinicalTrials.gov NCT01803958).

Material/Methods:

This randomized, non- inferiority phase III trial recruited patients in 35 centres. Women aged ≥ 49 years with invasive breast cancer <3 cm, pN0-1, were randomly assigned after breast-conserving surgery to 3D-CRT APBI (38.5 Gy in 10 fractions twice daily) or WBI. Patients received adjuvant systemic therapy according to institutional guidelines. The primary endpoint was ipsilateral breast tumour recurrence (IBTR) at 5 years. Secondary endpoints include distant metastasis-free survival (DMFS) and overall survival (OS). Analyses were performed based on intention-to-treat.

Results:

From March 2007 to March 2019, 3309 patients were randomly assigned to WBI (1657) and APBI (1652). After random assignment, 50 patients assigned to the APBI arm and 34 to the WBI arm were excluded from intention-to treat analysis because of consent withdrawal, protocol deviation (misinterpretation of the eligibility criteria), or loss to follow-up. The intention-to-treat population comprised 3225 patients (1623 for WBI and 1602 for APBI). Baseline patient characteristics are reported in Tables 1-2. Median follow-up was 96.1 months (IQR 67.1-121.7). The 5-year cumulative incidence of IBTR was 0.9% (95% CI 0.5 – 1.4) in the APBI group vs 0.7% (0.4 – 1.3) in the WBI group (HR 1.56 [90% CI 0.87 – 2.77], n.s.). The 5-year DMFS was 98.6% (99.1 – 97.9) in the APBI group vs 98.7% (99.2 – 98) in the WBI group. The 5-year OS was 98.6% (99.1 – 97.9) in the APBI group vs 98.4% (99 – 97.7) in the WBI group.