ESTRO 2025 - Abstract Book

S1163

Clinical – Lower GI

ESTRO 2025

≥ 3 acute toxicity (P=0.51). Dermatitis radiation grade 3 (n=5, 8.2%) was most reported. No grade 4-5 acute toxicity was observed. Only 1 patient (2.9%) developed a grade 1 burn related to HT. During HT treatments, 24 patients (70.6%) experienced general mild pain, 12 patients (35.3%) warm skin, 7 patients 7 (20.6%) bolus pressure, and 5 patients (14.7%) mild discomfort. Overall, Thirty-one patients (91.2%) received 2 HT sessions and 3 patients (8.8%) received 1 HT session. Furthermore, about postoperative complications, nine patients (14.8%) developed postoperative complications, 6 (9.8%) in the SCRT plus TNT-ChT plus HT group and 3 (4.9%) in the SCRT plus TNT ChT alone (P=0.72). Conclusion: This prospective phase II trial for LARC patients showed a clinically relevant increase of 10% in pathological complete response rates in patients treated with short course radiotherapy plus total neoadyuvant chemotherapy combined with locoregional deep hyperthermia, mostly with mild toxicities, good tolerance and adherence.

Keywords: Rectal-Cancer, Hyperthermia, Pathological-response

1116

Proffered Paper PRIME-RT: Durvalumab with extended neoadjuvant regimens in locally advanced rectal cancer (LARC): a randomised phase II trial Campbell S Roxburgh 1 , Catherine R Hanna 1 , Mark P Saunders 2 , Claire Arthur 2 , Leslie M Samuel 3 , Lucy Wells 3 , Rebecca Muirhead 4 , Nicholas J MacLeod 5 , Janet S Graham 6 , Lynsey Devlin 7 , Joanne Edwards 1 , Lily V Hillson 1 , Ross K McMahon 1 , Ashley K McCulloch 1 , Lucy Paterson 8 , Caroline Kelly 8 , Liz-Anne Lewsley 8 , Nicola Walker 8 , Richard Adams 9 , Sean M O'Cathail 7 1 School of Cancer Sciences, University of Glasgow, Glasgow, United Kingdom. 2 Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 3 Department of Oncology, University of Aberdeen, Aberdeen, United Kingdom. 4 Department of Oncology, Oxford University Hospitals NHS Trust, Oxford, United Kingdom. 5 Clinical Oncology, Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 6 Department of Medical Oncology, Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 7 Department of Clinical Oncology, Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 8 Glasgow Oncology Clinical Trials Unit, Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 9 Department of Oncology, Velindre Cancer Centre, Cardiff, United Kingdom Purpose/Objective: Standard care of mismatch-repair (MMR) proficient LARC involves short (SC) and long-course (LC) neoadjuvant radiotherapy (RT). RT induces immune changes within the tumour, but each regimen is hypothesised to differ. PRIME-RT tests inclusion of Durvalumab (Durv) immunotherapy to both SC and LC-based total neoadjuvant therapy (TNT) aiming to enhance complete response (CR) rates and organ preservation. Material/Methods: Multi-centre, randomised phase-II trial (pick-the-winner). Following safety run-in, the main trial recruited patients (pts) with LARC (cT3b+,N+,EMVI+ on MRI or tumours requiring APR) randomised to Arm A: SC-RT(25Gy in 5 fractions) with Durv, followed by Durv-FOLFOX, or Arm B: LC-RT(50Gy in 25 fractions + capecitabine) with Durv followed by Durv-FOLFOX. Primary endpoint was CR rate (pathological or clinical (pCR/cCR) entering active surveillance) at end of-treatment (EOT-6 months). Treatment was considered effective if >30% exhibit CR. Serial tumour/blood samples were collected to track evolution of RT-immunotherapy responses.