ESTRO 2025 - Abstract Book

S1244

Clinical – Lower GI

ESTRO 2025

Conclusion: The present work confirms that the SCRT strategy is a valuable option for the treatment of rectal cancer both in case of LARC and metastatic disease. Further investigation is warranted to find pts who could most benefit from this approach and the best timing between RT and surgery.

Keywords: Rectal Cancer, Short Course Radioterapy, Surgery

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Digital Poster Risk-Stratified Follow-up in Rectal Cancer Patients with Clinical Complete Response: A Tailored Approach from Watch-and-Wait Strategy Chen Yang 1,2 , Yizhe Cheng 1,2 , Peijun Wei 1,2 , Qiaoxuan Wang 1,2 , Xue Tian 1,2 , Zitong Zhang 1,2 , Liren Li 3,2 , Rong Zhang 4,2 , Yuanhong Gao 1,2 1 Radiation Oncology, Sun Yat-sen University Cancer Center, Guangzhou, China. 2 Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University Cancer Center, Guangzhou, China. 3 Colorectal Surgery, Sun Yat sen University Cancer Center, Guangzhou, China. 4 Endoscopy, Sun Yat-sen University Cancer Center, Guangzhou, China Purpose/Objective: The watch-and-wait (W&W) strategy is increasingly used for rectal cancer patients achieving clinical complete response (cCR) after neoadjuvant chemoradiation (NCRT). Magnetic resonance imaging (MRI) plays a pivotal role in risk stratification, distinguishing high-risk from low-risk patients based on tumor characteristics. However, optimal follow-up strategies based on MRI-defined risk levels remain non-standardized. This study aimed to evaluate follow up strategies and survival outcomes in MRI risk-stratified rectal cancer patients under the W&W approach. Material/Methods: A retrospective cohort of 153 patients with non-metastatic rectal adenocarcinoma who achieved cCR after NCRT and underwent W&W between 2006 and 2021 was analyzed. High-risk patients were defined by baseline MRI features such as cT3c–d/T4a–b, cN2, clinically positive lateral nodes, positive mesorectal fascia, and extramural vascular invasion. Survival outcomes and cumulative incidence of local regrowth and distant metastasis were assessed using Kaplan-Meier and competing risks methods. A theoretical comparison of different follow-up schedules was conducted. Results: The median follow-up time was 62.5 months (95% CI, 57.3–67.7). The 5-year overall survival rates were similar between high-risk and low-risk groups (89.3% vs. 91.1%). However, significant differences were observed in disease free survival, non-regrowth disease-free survival, and distant metastasis-free survival ( P = 0.0082, P = 0.0034, P = 0.0053, respectively). High-risk patients had a significantly higher 5-year cumulative incidence of distant metastasis (21.7% vs. 3.3%, P = 0.003), but no significant difference in local regrowth (10.2% vs. 9.4%, P = 0.380). Among the 24 patients who developed distant metastasis, 22 (91.7%) were from the high-risk group, with 16 (72.7%) having subclinical metastasis without local regrowth. The theoretical follow-up comparison suggested that the optimal strategy should include 3-monthly endoscopy and 6-monthly MRI in the first two years for all patients, with 3 monthly chest-abdominal computed tomography (CT) in the first three years for high-risk patients to detect distant metastasis early. Conclusion: MRI-based risk stratification for follow-up is feasible in the W&W approach and improves monitoring efficiency while reducing costs. This strategy can optimize patient management and enhance outcomes for rectal cancer patients with cCR after NCRT.