ESTRO 2025 - Abstract Book

S1192

Clinical – Lower GI

ESTRO 2025

Material/Methods: Patients receiving TNT with consolidation chemotherapy for LARC (UICC Stage II/III) between 2015 and 2023 across 21 centers from Germany and Austria were included. The primary endpoint was pathological CR. Secondary endpoints comprised toxicity (according to CTCAE v5.0), tumor control and number of deaths. We analyzed the association of the primary endpoint with the TNT regimen (CRT versus SCRT) with generalized estimating equations (GEE), accounting for multicentricity and adjusting for ESMO risk category [4], TNT duration, age and sex. We excluded centers with <5 patients to ensure model stability, and provide adjusted OR, 95% CI and p-values. Results: We included 282 patients. Their median age at diagnosis was 62 (range: 24-85) years, 201 (71.3%) were male, and 157 (55.7%) underwent CRT. According to the ESMO risk category, 24 (16.1%) and 78 (52.3%) of 149 CRT patients versus 26 (21.8%) and 76 (63.9%) of 119 SCRT patients had “bad” and “advanced” LARC, respectively. CR was achieved in 88 (56.1%) CRT patients and 47 (37.6%) SCRT patients. Among them, NOM was documented for 45/80 (56.3%) CRT and 13/46 (28.3%) SCRT patients. GEE modeling (258 patients / 17 centers) revealed a higher likelihood for CR after CRT (1.95, 1.24-3.08, p=0.004) and per additional month of TNT (1.64, 1.35-1.99, p<0.001). Furthermore CR was associated with ESMO risk category and age (p<0.001 and p=0.039, respectively). Evidence for an influence of sex was not observed (p>0.05). The most frequent CTCAE grade 3/4 events were leukopenia (CRT: 18/153 (11.8%) versus SCRT: 5/91 (5.5%) patients), neutropenia (11/133 (8.3%) versus 4/82 (4.9%)) and diarrhea (11/155 (7.1%) versus 5/111 (4.5%)). After a median follow-up since treatment initiation of 19.6 (CRT, Q1-Q3: 14.8-31.8) and 19.3 (SCRT, Q1-Q3 13.2-27.5) months, local and distant recurrences occurred in totaled 29/147 (19.7%) CRT and 23/120 (19.2%) SCRT patients, with cancer-related deaths affecting 10/147 (6.8%) and 4/120 (3.3%) patients, respectively. Conclusion: Preliminary results of this multicenter analysis suggest an increased likelihood of CR after CRT within the TNT approach. Future research on the impact of the TNT regimen is warranted. Keywords: total neoadjuvant therapy, rectal cancer References: 1. Bahadoer et al., The Lancet Oncology, 2021. 22 (1): p. 29-42. DOI: 10.1016/S1470-2045(20)30555-6 2. Conroy et al., The Lancet Oncology, 2021. 22 (5): p. 702-715. DOI: 10.1016/S1470-2045(21)00079-6 3. Fokas et al., Journal of Clinical Oncology, 2019. 37 (34): p. 3212-3222. DOI:10.1200/JCO.19.00308 4. Glynne-Jones et al ., Annals of Oncology, 2017. 28 : p. iv22-iv40. DOI: 10.1093/annonc/mdx224 Proffered Paper ARISTOTLE: Mature results of a phase 3 trial evaluating the addition of irinotecan to capecitabine chemoradiation in locally advanced rectal cancer David Sebag-Montefiore 1 , Leslie Samuel 2 , Simon Gollins 3 , Robert Glynne-Jones 4 , Robert Harte 2 , Nicholas West 1 , Philip Quirke 1 , Arthur Sun Myint 5 , Simon Bach 6 , Stephen Falk 7 , Philip Parsons 8 , Amandeep Dhadda 9 , Vivek Misra 10 , Gina Brown 11 , Mark Harrison 4 , Laura White 12 , Marian Duggan 12 , Rubina Begum 12 , Elizabeth Chang 12 , Rukan Musleh 12 , Andre Lopes 12 , Richard Adams 13 1 Leeds Institute of Medical Research at St. James's, University of Leeds, Leeds, United Kingdom. 2 Clinical Oncology, Aberdeen Royal Infirmary, Aberdeen, United Kingdom. 3 Clinical Oncology, Shrewsbury and Telford NHS Trust, Shrewsbury, United Kingdom. 4 Clinical Oncology, Mount Vernon Hospital, Rickmansworth, United Kingdom. 5 Clinical Oncology, Clatterbridge Cancer Centre NHS Trust, Liverpool, United Kingdom. 6 Department of Surgery, University Hospitals Birmingham, Birminghan, United Kingdom. 7 Clinical Oncology, Bristol Haematology and Oncology Centre, Bristol, United Kingdom. 8 Department of Physics, Velindre NHS Trust, Cardiff, United Kingdom. 9 Clinical Oncology, Castle Hill Hospital, Hull, United Kingdom. 10 Clinical Oncology, Christie NHS Foundation Trust, Cardiff, United 2186