ESTRO 2021 Abstract Book

S982

ESTRO 2021

D. Muñoz Guglielmetti 1 , D. Sánchez 2 , R. Reyes 3 , M. Boada 2 , J. Mases 1 , M. Mollà 1 , F. Casas 1 1 Hospital Clínic de Barcelona, Radiation Oncology, Barcelona, Spain; 2 Hospital Clínic de Barcelona, Thoracic Surgery, Barcelona, Spain; 3 Hospital Clínic de Barcelona, Medical Oncology, Barcelona, Spain Purpose or Objective Neoadjuvant treatment (NT) with chemotherapy (Ch) is considered a standard option for resectable stage III (N2) NSCLC. Several studies have suggested an additional benefit to add radiotherapy (RT) in the NT with Ch. The International Association for the Study of Lung Cancer (IASLC) published a recommendation for the pathological evaluation of NSCLC resection specimens after NT. Our objective is to contribute to these recommendations comparing our experience with the response to NT Ch versus NT ChRT. Materials and Methods We analyzed 67 consecutive patients with resectable stage III NSCLC (TNM 8th edition) with positive mediastinal node treated between 2012 and 2020 with radical surgery after NT. The radiological response (RR) was assessed by CT scan (RECIST criteria) after NT. Patients without disease progression (DP) during NT underwent surgery. The pathological response (PR) was assessed by the percentage of viable cells in the tumor and in the resected lymph nodes. The latter was used to assess downstaging. The statistical analysis was carried out through the IBM SPSS version 25.0 Results 40 patients underwent ChRT and 27 Ch, the clinical characteristics are represented in Table 1. 56 (83.6%) patients underwent surgery (35 ChRT and 21 Ch). 5 ChRT patients did not undergo surgery (2 due to poor respiratory function, 1 brain progression, 1 severe respiratory infection, 1 with high pneumonectomy risk) and 6 in the Ch group (3 local progression during Ch, 1 with high pneumectomy risk, and 2 due poor NT Ch response). The median time from ChRT to surgery was 6 weeks (3-19) and 8 week (3-21) for Ch patients. 3 patients were included in the study (2 with N3 and 1 with solitary brain metastasis treated with radiosurgery) who underwent salvage surgery by decision of a multidisciplinary committee. We observe significant differences in RR, with DP in 2.5% and 14.8% of patients with ChRT and Ch, respectively, and partial response in 62.5% ChRT vs 29.6% Ch (p = 0.025). In PR we observed ≤10% viable cells in the tumor in 19 (54.4%) and 2 (9.5%), and in the resected lymph nodes 30 (85.7%) and 7 (33.3%) in ChRT and Ch, respectively (p= 0.001), with higher rates of downstaging in the ChRT group (80% vs 33.3%; p= 0.002). The evaluation of the response is summarized in Table 2. A higher proportion of patients was observed in the ChRT group that required admission due to toxicity after NT (20% vs 7.4%; p = 0.15). Only 2 of 67 patients had grade 3 esophagitis and no symptomatic pneumonitis was observed.