ESTRO 2025 - Abstract Book

S1211

Clinical – Lower GI

ESTRO 2025

3.Theophanous S, et al. Prognostic factors for patients with anal cancer treated with conformal radiotherapy-a systematic review. BMC Cancer. 2022 Jun 3;22(1):607. 4. Sauter C, et al. Influence of radiation treatment technique (IMRT vs. 3D-RT) on acute toxicity and prognostic factors for survival for anal cancer. Sci Rep. 2022 Nov 19;12(1):19914.

2500

Proffered Paper Factors influencing locoregional recurrence rates in rectal cancer after total neoadjuvant treatment versus chemoradiotherapy in the RAPIDO trial Ilaria Prata 1,2,3 , Max D. Tanaka 4 , Bengt Glimelius 5 , Iris D. Nagtegaal 6 , Regina G.H. Beets-Tan 1,7,8 , Lennart K. Blomqvist 9 , Alice M. Couwenberg 4 , Boudewijn van Etten 10 , Geke A.P. Hospers 11 , Elma Meershoek - Klein Kranenbarg 3 , Koen C.M.J. Peeters 3 , Hein Putter 12 , Annet G.H. Roodvoets 3 , Cornelis J.H. van de Velde 3 , Per J. Nilsson 13 , Corrie A.M. Marijnen 4,14 1 GROW, School of Oncology and Reproduction, Maastricht University, Maastricht, Netherlands. 2 Surgery, Netherlands Cancer Institute, Amsterdam, Netherlands. 3 Surgery, Leiden University Medical Center, Leiden, Netherlands. 4 Radiation Oncology, Netherlands Cancer Institute, Amsterdam, Netherlands. 5 Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden. 6 Pathology, Radboud University Medical Center, Nijmegen, Netherlands. 7 Radiology, Netherlands Cancer Institute, Amsterdam, Netherlands. 8 Radiology, University of Southern Denmark, Odense, Denmark. 9 Nuclear Medicine/Radiation Physics, Karolinska University Hospital, Stockholm, Sweden. 10 Surgery, University Medical Center Groningen, Groningen, Netherlands. 11 Medical Oncology, University Medical Center Groningen, Groningen, Netherlands. 12 Medical Statistics and Bioinformatics, Leiden University Medical Center, Leiden, Netherlands. 13 Pelvic Cancer, Karolinska University Hospital, Stockholm, Sweden. 14 Radiation Oncology, Leiden University Medical Center, Leiden, Netherlands Purpose/Objective: The international phase III RAPIDO trial demonstrated that short-course radiotherapy (SCRT) followed by preoperative chemotherapy (total neoadjuvant treatment (TNT)) reduced distant metastases and doubled pathological complete response rates compared to long-course preoperative chemoradiotherapy (CRT) with optional postoperative chemotherapy in patients with locally advanced rectal cancer (LARC). However, a higher locoregional recurrence (LRR) rate was observed after TNT. We investigated which factors contributed to the difference in LRR between TNT and CRT. Material/Methods: Patients with high-risk LARC were randomised between TNT (5x5 Gy followed by 6xCAPOX or 9xFOLFOX4) and CRT (25-28x1.8-2 Gy with concurrent capecitabine). Protocolised time between start of TNT or CRT and surgery was 24 and 13 weeks, respectively. Patients who underwent a local R0/1 resection were included in the current study. Sphincter-preserving surgery (SPS) was defined as either (low) anterior resection or Hartmann’s procedure. The influence of baseline, treatment, response, and histopathological characteristics on LRR was evaluated (Figure 1). Cause-specific Hazard Ratios (HR) and interactions between variables of interest and treatment groups were calculated with Cox regression, accounting for all causes of death as a competing risk. Results: Of 920 randomised patients, 849 (430 in the TNT and 419 in the CRT group) were eligible for the present analyses. After a median follow-up of 8 years, overall LRR rates were 11% (46/430) after TNT and 6% (24/419) after CRT [HR 1.91 (1.17-3.13), p=0.010]. For Swedish patients (n=315) no difference was observed in LRR between TNT and CRT (8% in both groups), whereas these proportions were 12% (TNT) and 4% (CRT) in the other countries [P interaction =0.08]. Following SPS, 12% (TNT) and 5% (CRT) of patients developed a LRR, compared to 8% vs. 7%, respectively, after APR [P interaction =0.13]. The proportions of patients with SPS and distal margin ≤10mm were similar between the TNT and CRT groups (18%, 47/262 vs . 23%, 56/242, respectively), however, in these patients a higher LRR rate was observed