ESTRO 2025 - Abstract Book

S1198

Clinical – Lower GI

ESTRO 2025

cycle-dose-equivalents (CDE) based on one FOLFOX4 cycle to enable comparability between different protocols. The association of CR (primary endpoint) with CDE and TNT duration was analyzed with generalized estimation equations (GEE), accounting for multicentricity. Centers with <5 patients were excluded to ensure model stability. This model was adjusted for perceived treatment (short-course radiotherapy / chemoradiotherapy), patient’s age, sex and ESMO tumor risk category [4]. Similarly, we analyzed the secondary endpoint acute toxicity (assessed per CTCAE v5.0), but without ESMO tumor risk category. We provide adjusted OR with 95% CI and p-value. Results: A total of 282 patients (201 (71.3%) men) were included. The median age at diagnosis was 62 (range 24-85) years, and 135 (47.9%) achieved CR. A median number of 6 (range 1-14) cycles of consolidation chemotherapy, predominantly consisting of FOLFOX (64.2%) or CapOx (32.8%), was administered. The median TNT duration was 4.7 (range 0.3-8.5) months in CR patients and 4.3 (range 0.6-11.6) months in non-CR patients. In GEE modeling (241 patients / 17 centers), we identified an increased likelihood for CR in chemoradiotherapy patients (2.27 (1.34-3.86), p=0.002), for female sex (1.82 (1.09-3.05), p=0.023), per additional CDE of 5-fluorouracil (1.13 (1.03-1.23), p=0.011) and oxaliplatin (1.15 (1.03 1.28), p=0.014). ESMO risk category was associated with CR (p<0.001). Severe toxicity (CTCAE grade 3/4) was reported for 81/276 (29.3%) patients; the likelihood for its occurrence increased per additional chemotherapy cycle (1.67 (1.42-1.97), p<0.001) in GEE modeling (242 patients / 17 centers). Additional 10 years of patient age (1.58 (1.19-2.10), p=0.002) and CRT (16.22 (7.47-35.19), p<0.001) also increased this likelihood. Unexpectedly, the likelihood decreased per additional oxaliplatin CDE (0.71 (0.59-0.85), p<0.001) and 5-fluorouracil CDE (0.76 (0.65-0.88), p<0.001). Conclusion: This preliminary analysis suggests an association of higher cumulative chemotherapy doses with CR. Severe toxicity may depend on treatment intensity (chemoradiotherapy, chemotherapy cycles) and age, whereas the unexpected effect directions of CDE might be related to data heterogeneity. Further in-depth analyses are pending.

Keywords: rectal cancer, TNT, chemotherapy dose

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

2250

Proffered Paper Short-term radiotherapy plus chemotherapy for locally advanced rectal cancer: 5-year outcomes of the phase III clinical trial (NCT02533271) Yuan Tang 1 , Haitao Zhou 2 , Tongzhen Xu 1 , Ning Li 3,1 , Yong Cai 4 , Yong-Heng Li 4 , Yuan Zhu 5 , Ming-Yuan He 6 , Xin Wang 7 , Ke Liu 8 , Hong-Yan Zhang 9 , Jun Wang 10 , Ting Zhao 11 , Jia-Lin Yang 12 , Kuan Zhang 13 , Wen-Ling Wang 14 , Shulian Wang 1 , Hai-Zeng Zhang 2 , Xi-Shan Wang 2 , Chen Hu 15 , Li-Chun Wei 16 , Shi-Xin Liu 17 , Yuan-Hong Gao 18 , Ye-Xiong Li 1 , Jing Jin 19,1 1 State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China. 2 State Key Laboratory of Molecular Oncology and Department of Colorectal Surgery, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China. 3 Department of Radiobiology, Shanxi Province Cancer Hospital/ Shanxi Hospital Affiliated to Cancer Hospital, Chinese Academy of Medical Sciences/Cancer Hospital Affiliated to Shanxi Medical University, Taiyuan, China. 4 Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Department of Radiation Oncology, Peking University