ESTRO 2025 - Abstract Book

S626

Clinical - Breast

ESTRO 2025

Conclusion : Disparities in radiotherapy adherence point to a need for improved categorisation of non-adherence reasons and consistent patient support across Denmark

Keywords: radiotheraphy, disparity, clinical trials

References: Cancerregistret. Nye Kræfttilfælde i Danmark 2018. Sundhedsdatastyrelsen. Thorsen LB et al. Int. Mam Node Irradiation. J Clin Onc. 2016;34(4):314-20. Thorsen LBJ et al. 15-Year Results. J Clin Oncol. 2022;40(36):4198-4206. Ejlertsen B et al. Forty Years of DBCG Trials. Acta Onc. 2018;57(1):3-12. Overgaard M et al. Radioth. in High-Risk BC. Lancet. 1999;353:1641-8. Overgaard M et al. Radioth. in Premenop Women. N Engl J Med. 1997;337(14):949-55. Overgaard M et al. 30-Year DBCG Rep. Radiother Oncol. 2022;170:4-13. Kerba M et al. Benchmark Need. Clin Oncol. 2007;19:481-9. Shack L et al. Radioth Need. Radiother Oncol. 2017;122:152-8. MacKenzie P et al. Adjusted Rate. J Geriatr Onc. 2022;13:844-9. Round CE et al. Demand. Clin Onc. 2013;25:522-30

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Digital Poster Safety of Concurrent TDM1 and Locoregional Radiotherapy in HER2-Positive Breast Cancer: A Retrospective Analysis Arnaud BEDDOK 1 , Laura Girres 2 , Paolo Torielli 1 , Estelle Vigneau 1 , Leila Ettalhaoui 1 , Sofiane Guendouzen 1 , Judicael Hotton 3 , Christelle Jouannaud 2 , Amélie Lemoine 2 , Damien Parent 4 , Pauline Soibinet 2 , Stéphane Vignot 2 , Philippe Guilbert 1 1 Radiation Oncology, Godinot, Reims, France. 2 Medical Oncology, Godinot, Reims, France. 3 Breast oncology surgery, Godinot, Reims, France. 4 Pharmacy, Godinot, Reims, France Purpose/Objective: This study evaluated the safety of concurrent trastuzumab emtansine (TDM1) and locoregional radiation therapy (RT) in non-metastatic HER2-positive breast cancer patients with residual disease after neoadjuvant chemotherapy, with a focus on the risk of radiation-induced pneumonitis (RIP). Material/Methods: A retrospective cohort of 31 patients treated between April 2021 and September 2023 with TDM1 and concurrent RT at Institut Godinot was analyzed. Eligibility required residual invasive disease in the breast or axilla post-neoadjuvant chemotherapy (RCB ≥1). Acute and late toxicities were assessed using CTCAE v5.0, and lung computed tomography was performed in symptomatic patients to evaluate RIP. Statistical analyses used Chi-square or Fisher’s exact tests for categorical variables and Mann-Whitney U for continuous variables, with significance set at p<0.05. Results: The median age was 63 years (IQR: 46–69); nine patients were smokers (five active), and three had chronic pulmonary diseases (asthma or COPD). The median RT dose was 50 Gy (IQR: 50–50.4 Gy), with lymph node irradiation in 25/31 patients and a tumor bed boost in 22/31. Median PTV was 679.8 cc (IQR: 586.8–1079.9). Dosimetric data included ipsilateral lung mean dose (median: 13.4 Gy; IQR: 11.1–14.7) and V20 (median: 26%; IQR: 16–26). TDM1 was administered for a median of 7.5 months (IQR: 6.75–8), with a median concurrent RT duration of 42 days (IQR: 38–48). Grade ≥2 acute dermatitis occurred in 30% of patients. RIP grade ≥2 was reported in 19.35% (6/31) within two months of RT, with one grade 3 case requiring early TDM1 cessation. Univariate analysis identified chronic pulmonary disease as a significant risk factor for RIP (p=0.02), but dosimetric factors (mean lung dose, V20) were not predictive. No grade 5 toxicities were reported. After a median follow-up of 23 months (IQR: 13.5–34), late toxicities of grade ≥1 were observed in 22.58%, with grade ≥2 in 6.45%. Most frequent late toxicities included mild breast fibrosis and arm lymphedema.