S731
Clinical – Lower GI
ESTRO 2026
and chemoradiotherapy for locally advanced rectal cancer (UNICANCER-PRODIGE 23): phase 3 trial. Lancet Oncol. 2021;22(5):702–715.3. Garcia-Aguilar J, Patil S, Gollub MJ, Kim JK, Yuval JB, Thompson HM, et al. Organ preservation in patients with rectal adenocarcinoma treated with total neoadjuvant therapy. J Clin Oncol. 2022;40(23):2546–56. doi:10.1200/JCO.22.00032. Keywords: Radiotherapy, chemoradiotherapy, relapse
preservation strategies in rectal cancer, we conducted a descriptive analysis of patients with rectal adenocarcinoma treated with either long-course chemoradiotherapy (LRT) or short-course radiotherapy (SRT) at our center in the pre-Total Neoadjuvant Therapy (TNT) era. The main objectives were to determine the distribution of Mandard tumour regression grade (MRG) following surgery and identify clinical and treatment-related factors associated with achieving a good pathological response (MRG 1–2). Material/Methods: We retrospectively analyzed 238 consecutive patients treated between 2017 and 2022 with either LRT (50.4 Gy in 28 fractions + 5-FU or capecitabine) or SRT (25 Gy in 5 fractions). Clinical data were extracted from our center's database, and radiotherapy data from ARIA(©Varian). Follow-up was recorded from the end of radiotherapy until death or last medical appointment (cutoff: 31/10/2025). Results: Of the 238 patients, 234 were evaluable. The cohort included 164 males (70.1%) and 70 females (29.9%), median age 67 years (range: 38–91). Forty-nine patients (23%) received SRT, and 164 (77%) LRT. The average time from radiotherapy to surgery was 41 days for SRT and 63 for LRT. Post-neoadjuvant MRG for the entire cohort: MRG1 in 46 (21.5%), MRG2 in 63 (29.4%), MRG3 in 58 (27.1%), MRG4 in 42 (19.6%), and MRG5 in 5 (2.3%). By regimen: MRG1, 3.6% SRT vs. 19.8% LRT; MRG2, 5.2% SRT vs. 22.4% LRT; MRG3, 6.3% SRT vs. 21.9% LRT; MRG4, 7.3% SRT vs. 11.5% LRT. Median follow-up was 49 months (range: 2–99). During follow-up, 57 patients (25.6%) relapsed, and 166 (74.4%) did not (data unavailable for 15). Median time to relapse was 17 months (range: 1–88). A total of 160 patients (74.4%) were alive, and 55 (25.6%) died; 26 deaths (54.2%) were disease-related. Patients treated with LRT had significantly higher MRG1–2 rates (42.2% vs. 8.8%, p=0.013) and lower relapse probability (19.6% vs. 37.5%, p=0.011) compared to SRT. No significant associations were found between age or sex and tumour response (MRG) or mortality. Conclusion: LRT achieved higher MRG1–2 rates and fewer relapses than SRT, although in SRT the first years at our center the time from end of RT to surgery was not enough to evaluate the response. Also we did not categorize relapses as local or distant, Despite current TNT use in locally advanced rectal cancer, our MRG1–2 rate is consistent with other pre-TNT studies. References: 1. Bahadoer RR, Røstergaard L, et al. Short-course radiotherapy followed by chemotherapy before total mesorectal excision vs preoperative chemoradiotherapy in locally advanced rectal cancer (RAPIDO): phase 3 trial. Lancet Oncol. 2021;22(1):29– 42.2. Conroy T, Borg C, et al. Neoadjuvant FOLFIRINOX
Mini-Oral 3977
Acute toxicity and compliance using involved field and pelvic IMRT in anal squamous cell carcinoma: data from the PLATO ACT3 and ACT 4 clinical trials Andrew G Renehan 1,2 , Chloe Gaul 3 , Joanne C Webster 3 , Natalie Abbott 4 , Richard Adams 5 , Lindy Berkman 6 , Sarah Brown 3 , Joanne Copeland 3 , Alexandra Gilbert 7,8 , Duncan C Gilbert 9 , Rob Glynne-Jones 10 , Vicky Goh 11 , Mark Harrison 10 , Maria A Hawkins 12 , Sheela Rao 13 , Susan D Richman 8 , Sharon P Ruddock 3 , Alexandra F Smith 3 , David Sebag-Montefiore 7,8 , Rebecca Muirhead 14,15 1 Colorectal and Peritoneal Oncology Centre, The Christie NHS Foundation Trust, Manchester, United Kingdom. 2 Division of Cancer Sciences, University of Manchester, Manchester, United Kingdom. 3 Leeds Cancer Research UK Clinical Trials Unit, Leeds Institute of Clinical Trials Research, Leeds, United Kingdom. 4 National Radiotherapy Trials QA RTTQA Group, Cardiff University Heath Park, Cardiff, United Kingdom. 5 Centre for Trials Research, Cardiff University Heath Park, Cardiff, United Kingdom. 6 Patient Representative, NA, NA, United Kingdom. 7 Leeds Cancer Research UK Clinical Trials Unit, Leeds Institute of Clinical Trials Research,, Leeds, United Kingdom. 8 Leeds Institute of Medical Research at St James St., St. James University Hospital, Leeds, United Kingdom. 9 Sussex Cancer Centre, University Hospitals Sussex NHS Foundation Trust, Brighton, United Kingdom. 10 Mount Vernon Centre for Cancer Treatment, Mount Vernon Hospital, London, United Kingdom. 11 School of Biomedical Engineering & Imaging Sciences,, King's College London, London, United Kingdom. 12 Department of Medical Physics & Biomedical Engineering, University College London, London, United Kingdom. 13 The Royal Marsden Hospital, Institute of Cancer Research, London, United Kingdom. 14 Department of Oncology, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom. 15 Department of Oncology, University of Oxford, Oxford, United Kingdom Purpose/Objective: Despite the introduction of intensity modulated radiotherapy (IMRT) and reduced dose chemoradiotherapy (CRT) for anal squamous cell carcinoma (ASCC), the acute toxicity and compliance
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