ESTRO 2024 - Abstract Book

S533

Clinical - Breast

ESTRO 2024

Veronica Vernier 1,2 , Lorenzo Lo Faro 1,2 , Antonella Fogliata 1 , Davide Franceschini 1 , Ruggero Spoto 1 , Luca Dominici 1 , Sara Stefanini 1,2 , Mariya I. Boyanova 1,2 , Marta Scorsetti 1,2 1 IRCCS Humanitas Research Hospital, Department of Radiotherapy and Radiosurgery, Rozzano (MI), Italy. 2 Humanitas University, Department of Biomedical Sciences, Pieve Emanuele (MI), Italy

Purpose/Objective:

Therapeutical strategies in breast cancer are continuously updating. Recent research assessed the possibility of irradiating only the surgical bed in selected patients (Accelerated Partial Breast Irradiation, APBI), without differences in nodal and systemic recurrence, overall survival (OS), and disease-specific mortality compared with whole breast irradiation (WBI). Since there were heterogeneous pool of techniques and doses in literature, in 2014 HYPAB trial was designed to evaluate toxicity and cosmesis of APBI using Volumetric Modulated Arc Therapy-Rapid Arc (VMAT-RA), compared with hypofractionated WBI.

Material/Methods:

HYPAB was a single-institution randomized phase III trial that recruited 172 patients from 2015 to 2018. All patients underwent conserving surgery and were randomized with a 1:1 ratio to either adjuvant WBI or APBI, both delivered with VMAT-RA technique. Post-menopausal women were included, with a histological confirmed early-stage breast cancer; in the WBI arm the entire mammary gland was irradiated with a total dose of 40.5 Gy in 15 fractions, while for APBI arm 30 Gy were delivered in 5 fractions on alternate days on the surgical bed only. Primary endpoints of the analysis were toxicity and cosmesis. Secondary endpoints included Local Control, Disease free survival and Overall survival. Clinical evaluation was performed during the first visit, at the simulation CT, once a week during radiotherapy and during follow up. Cosmesis was assessed using the Harvard Scale for Breast Cosmesis, while toxicities were evaluated according to the Common Terminology Criteria for Adverse Events (CTCAE) score v. 4.0. During follow up clinical and radiological evaluation of locoregional or systemic relapse of disease was performed.

Results:

At the time of the analysis 161 patients were eligible, 53% in the WBI and 47% in the APBI group, with a median follow-up of 67 months. Most common late skin toxicities were G1 fibrosis (32%) and oedema (28%) and were higher in the WBI group; no G3 toxicities were observed. At last follow up cosmesis was rated excellent in 21 cases (11 APBI, 10 WBI), good in 134 patients (64 APBI, 70 WBI) and poor in the remnant 6 cases. Of the 161 analyzed patients, 6 (3.7%) presented only local failure, 1 isolated axillary relapse (0.6%), 3 (1.8%) developed distant metastases, and one (0.6%) had both local and axillary progression; 147 patients had no evidence of disease at the last follow-up, and no patients died of the disease. DFS at 5 and 7 years was 95.6 ± 1.6 %, without statistically significant difference between the two groups. The estimated mean survival rate was 90.6 ± 0.4 %, with a 95% confidence interval between 89.7 and 91.4 %.

Conclusion: