ESTRO 2025 - Abstract Book

S1272

Clinical – Lower GI

ESTRO 2025

4149

Digital Poster IMPACT OF LATERAL LYMPH NODES ON CLINICAL OUTCOMES IN NEOADJUVANT RADIOCHEMOTHERAPY FOR LOCALLY ADVANCED RECTAL CANCER: A MONOINSTITUTIONAL EXPERIENCE Marco Lucarelli 1 , Giulia de Pasquale 1 , Rosario Bonelli 1 , Monica Di Tommaso 1 , Marianna Trignani 1 , Consuelo Rosa 1 , Andrea D'Aviero 1,2 , Domenico Genovesi 1,2 1 Department of Radiation Oncology, "S.S. Annunziata" Hospital, Chieti, Italy. 2 Department of Medical, Oral and Biotechnological Sciences, “G. D’Annunzio” University of Chieti, Chieti, Italy Purpose/Objective: Neoadjuvant Chemoradiotherapy (CRT) followed by Total Mesorectal Excision is the standard of care approach in Locally Advanced Rectal Cancer (LARC). However, postoperative recurrences and metastases are the main causes of treatment failures. Lymph node involvement is is the main pathway of metastatic diffusion in LARC. Clinical results published in literature reported the impact of pre- and post-treatment Lateral Lymph nodes (LLNs) positivity on clinical outcomes. Aim of this mono-institutional experience was to analyze the impact of LLNs involvment on Local Control (LC) and on Disease Free Survival (DFS) in our 10 years’ experience. Material/Methods: Data of 115 patients with LARC undergoing CRT from 2015 to 2024, were retrospectively analyzed. The presence of metastatic lymph nodes and the clinical persistence following CRT were evaluated with MRI. A first evaluation was conducted on patients with versus without pretreatment LLNs (LLNs+ vs LLNs-, respectively). A second analysis was conducted following post-CRT re-staging MRI restaging focusing on post-treatment positive LLN (yLLN+) versus no evidence of post treatment positive LLN (yLLN-). We used the LLN cut-offs according to Ogura et al. and Sluckin et al. 1,2 : pre-treatment pathological lymph nodes short axis ≥7 mm and post-treatment pathological lymph nodes short axis ≥4 mm. The Mantel-Cox method was used to estimate DFS and LC. A P-value less than 0.05 was considered statistically significant. Results: The median age of patients was 67 years (F: 41 and M: 75). Pre-treatment LLNs were detected in 18 patients (range of 8-18 mm) at baseline MRI. Regarding to LLNs locations, a prevalence was detected for internal iliac lymph nodes. The first analysis between LLNs+ vs LLNs- groups showed promising results for LC and DFS with p-values=0.10 and 0.20, respectively (fig. 1).