ESTRO 2023 - Abstract Book

S999

Digital Posters

ESTRO 2023

PO-1248 Outcomes of hypofractionated locoregional radiotherapy in advanced breast cancer

R. Tummineri 1 , A. Fodor 1 , F. Zerbetto 1 , M. Midulla 1 , M. Pasetti 1 , C.L. Deantoni 1 , R. Castriconi 2 , P. Mangili 2 , A. Del Vecchio 2 , N.G. Di Muzio 3 1 IRCCS San Raffaele Scientific Institute, Radiation Oncology, Milano, Italy; 2 IRCCS San Raffaele Scientific Institute, Medical Physics, Milano, Italy; 3 Vita-Salute San Raffaele University, Radiation Oncology, Milano, Italy Purpose or Objective Hypofractionated radiotherapy (HRT) is considered the standard treatment for breast cancer (BCa), but is generally applied for breast only RT. We report acute and late toxicity and outcomes in patients with advanced BCa treated with HRT to breast/chest wall (WBRT) and regional lymph-nodes (LN) in our Institute. Materials and Methods From 03/2018-03/2022 in our Institute 154 advanced BCa pts (2 bilateral, 98% female, 2% male) were treated with WBRT+LN HRT, after conservative surgery (56%) or mastectomy (42%), and as radical treatment (3 pts=2%). Median age was 52 (26 86) years. Molecular subtypes were: Luminal A 31%, Luminal B Her2- 31%, Luminal B Her+ 16%, HR negative Her2+ 13% and Triple negative 9%. Neoadjuvant chemotherapy (CHT) was prescribed in 52% of pts, adjuvant in 55%, and concomitant in 2.5%. Adjuvant hormonal therapy was prescribed in 77% of pts (IA or TMX -/+ LH-RH analogue), 31% of pts underwent HER2 targeted therapy. HRT was delivered with 3DCRT (10%), VMAT (30%) or Tomotherapy (60%), to a total dose of 40.05 Gy in 15 fractions, delivered in 3 weeks. Patients at high-risk of local relapse (34.5%) received simultaneous integrated boost (SIB) to 48 Gy to the tumor bed. The target was: WB+supra-clavicular (SCV) LN 35% (49% right, R, 51% left,L), WB+SCV+axillary LN 17% (44% R, 56% L), WB+SCV+axillary LN+internal mammary chain (CMI) 6% (44% R, 56% L), chest wall+SCV LN 29% (38% R, 62% L), chest wall+SCV+axillary LN 6% (22% R, 78% L), chest wall+SCV+axillary LN+CMI 7% (55% R, 45% L). Toxicity was registered according to CTCAE v 5.0. Results Median follow-up was 31 (7 – 68) months. No patient experienced ≥ G3 acute toxicity. G2 skin toxicity was experienced by 16% of pts with SIB and 7.5% without SIB. Pts evaluable for late toxicity and outcome were 152. Acute and late toxicities are summarized in table 1. No significant differences in acute and late toxicities were found between the different RT techniques. Patients undergoing CHT (95%) experienced higher acute skin toxicity (G2 12 vs 0%) and G1 dysphagia (57 vs 30%). Only one patient (metastatic at diagnosis and treated with radical WBRT+LN) had a local progression (local control rate was 99.4%), 14 pts had distant progression. Twelve, 24 and 36 months DPFS were 97.3%, 93.6% and 88.2% respectively (image 1a). Twelve pts were dead at the last follow-up, 10 for systemic progression, 2 for other causes. Thirty-six months OS was 93% (image 1b).

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