ESTRO 2020 Abstract book

S161 ESTRO 2020

This study aims to assess the efficacy of internal mammary nodal irradiation (IMNI) in patients with T1-2N1 breast cancer in the modern era and identify the specific subsets that benefit more from IMNI. Material and Methods Patients with T1-2N1 breast cancer treated during 1999 to 2016 at our institute were included. In order to determine the efficacy of IMNI, we only included patients received breast/chest wall and medial supraclavicular fossa irradiation. Patients not received adjuvant chemotherapy or treated with neoadjuvant chemotherapy were excluded. Patients with HER-2 overexpression disease not received Herceptin as adjuvant treatment were also excluded. The primary outcome was overall survival. Results A total 928 patients were included. The median follow-up was 98 months (range, 7 – 235 months). Among these patients, 649 patients received IMNI. The overall survival rates were similar between patients treated with IMNI and those not (HR 1.1, P = 0.58). In the subgroup analysis, patients with central/medial tumor (n = 321) did not significantly benefit from IMNI (HR 1.2, P = 0.7). IMNI also had no significant survival benefit in the subgroup of patients with ER negative disease, T2 disease or 2-3 metastatic axillary lymph nodes but had a trend for improved survival for patients with lymphovascular invasion disease (HR 0.61, P = 0.184). Patients aged between 45 and 54 years old (n = 332) treated with IMNI had improved overall survival. The 10-year overall survival for patients aged between 45 and 54 years old received IMNI was 95.1% compared to 79.6% for patients not (HR 0.3, P = 0.002). Among patients aged between 45 and 54 years old, only patients with nuclear grade 3 disease or 2-3 metastatic axillary lymph nodes significantly benefited from IMNI (HR 0.13, P < 0.001). The 10-year overall survival for this patient group (n = 246) was 96.3% for patients received IMNI and 65.8% for those not. After 1:1 propensity matching for this patients group, the survival benefit of IMNI remained.

Conclusion We present a workflow and results to derive radiation induced alopecia probability after cranial irradiation. To our knowledge this is the first study presenting data on temporary alopecia probability. After expanding the number of patient in the analysis, we envision that the observed relationship between alopecia and dose can be used to set soft constraints during treatment planning to improve quality of life for patients with primary or metastatic brain tumours.

Conclusion For patients with T1-2N1 breast cancer, a subset of patients aged between 45 and 54 years old, with nuclear grade 3 or 2-3 metastatic axillary lymph nodes may benefit from IMNI more. Further external validation is necessary.

Poster discussion: CL: Breast 2

PD-0290 Efficacy of internal mammary nodal irradiation in T1-2N1 breast cancer in the modern era C. Jen 1 , J. Yen 1 1 Koo Foundation Sun Yat-Sen Cancer Center, Department of Radiation Oncology, Taipei, Taiwan

Purpose or Objective