ESTRO 2025 - Abstract Book

S1166

Clinical – Lower GI

ESTRO 2025

Differences in operative time, resectability, surgical complications were secondary end-point. A matched paired control group was identified and a propensity score was applied. Univariate Χ 2 and multivarite Pearson’s covariance were used. Significance was fixed at p <0.05. Results: Twenty patients were identified (A group) who had received surgery after 14 mean weeks ( 13-16 wks) ; in the control group (B group), surgery after 10 mean weeks (8-12 wks)was allowed. All of them had been treated with long course nRCT (SIB -IMRT 1,8 Gy/45 Gy -2.2 Gy/55 Gy + concomitant capecitabine). The total response rate was 90% in the A group and 76 % in the B group ( p= 0.03). Complete pathological respone was 50% in A and 30% in B group (p=0.02). Time over 13.5 weeks ( 14-15 wks) was significant for the cPR (p <0.001), DWS ( p<0.003) and resectability (p<0.045). The operative time and intraoperative complications were better in the A group. Conclusion: The optimal timing for surgery after completion of nCRT for LARC to obtain tumor reduction , cPR and optimal rectability seems to be setted over 12 weeks. Eight weeks appears to be a critical threshold for optimal tumor response and surgical procedures. References: 1. Macchia G, Gambacorta MA, Masciocchi C, Chiloiro G, Mantello G, di Benedetto M, et al. Time to surgery and pathologic complete response after neoadjuvant chemoradiation in rectal cancer: a population study on 2094 patients. Clin Transl Radiat Oncol 2017;4:8–14. 2. Chiloiro G, Meldolesi E, Corvari B, Romano A, Barbaro B, Coco C, et al. BRIDGE -1 TRIAL: BReak Interval Delayed surgery for Gastrointestinal Extraperitoneal rectal cancer, a multicentric phase III randomized trial. Clin Transl Radiat Oncol 2022;8 :34–36. Mini-Oral De-escalating Anal Cancer Treatment (DeACT) in co-morbid and frail patients: A retrospective UK national service evaluation. Hamish Sinclair 1 , Michael Rowe 2 , Vinita Ruparel 3 , Laura Munn 4 , Timothy Mitchell 5 , Jin Tee 6 , Maya Bienz 7 , Jayaraj Erekkath 8 , Stuart Walter 9 , Chien Yin Gan 10 , Abhinav Vadapalli 11 , Alys Stevens 12 , Tee Lin Goh 13 , Charles Crocker 14 , Louisa Stockton 15 , Amy Irwin 16 , Sudha Karanam 17 , Philippa Smith 18 , Samira Bawany 19 , Oliver Coen 20 , The National Oncology Trainees Collaborative for Healthcare Research (NOTCH) 21 , Lindy Berkman 22 , Jessica Pearce 23 , Alexandra Gilbert 23 , Rebecca Muirhead 24 1 Clinical Oncology, University Hospitals Sussex NHS Foundation Trust, Brighton, United Kingdom. 2 Clinical Oncology, Royal Cornwall Hospitals NHS Trust, Truro, United Kingdom. 3 Clinical Oncology, Aberdeen Royal Infirmary, Aberdeen, United Kingdom. 4 Clinical Oncology, Royal Devon University Healthcare NHS Foundation Trust, Exeter, United Kingdom. 5 Clinical Oncology, Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 6 Clinical Oncology, Northern Ireland Cancer Centre, Belfast City Hospital, Belfast, United Kingdom. 7 Clinical Oncology, Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom. 8 Clinical Oncology, Imperial College Healthcare NHS Trust, London, United Kingdom. 9 Clinical Oncology, Edinburgh Cancer Centre, Western General Hospital, Edinburgh, United Kingdom. 10 Clinical Oncology, NHS Tayside, Dundee, United Kingdom. 11 Clinical Oncology, Royal Berkshire NHS Foundation Trust, Reading, United Kingdom. 12 Clinical Oncology, Singelton Hospital, Swansea, United Kingdom. 13 Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 14 Clinical Oncology, University Hospitals Bristol and Weston NHS Foundation Trust, Bristol, United Kingdom. 15 Clinical Oncology, University Hospitals Southampton NHS Foundation Trust, Southampton, United Kingdom. 16 Clinical Oncology, University Hospitals Birmingham NHS Foundation Trust, Birmingham, United Kingdom. 17 Clinical Keywords: resectability, pathological response, LARC 1435