ESTRO 2025 - Abstract Book

S1168

Clinical – Lower GI

ESTRO 2025

De-escalated treatment included standard-dose radiotherapy with reduced-dose chemotherapy (41%) or no chemotherapy (17%). Reduced dose or hypofractionated radical radiotherapy (EQD2 ≥30Gy) with chemotherapy (7%) and without chemotherapy (26%) and palliative radiotherapy alone (8%). Most patients (86%) completed radiotherapy as planned without treatment gaps. Of the 165 patients (165/338, 49%) who received chemotherapy, 73% (120/165) completed chemotherapy as planned, 16% (26/165) required a dose reduction, 2% (3/165) stopped chemotherapy early. A fifth of patients (21%) were admitted to hospital during or within 30 days of completing treatment. A 6-month post-treatment response assessment was performed on 272/338 (80%), of which 181/338 (53%) had a complete response. Follow-up data was available for 295 patients with a median follow-up of 59.3 months (95%CI 54.2-61.2). Frail patients had significantly reduced overall survival (median OS 28.6 months [95%CI 21.8-37.0] vs 51.9 months [95%CI 43.1-NR]) when compared to non-frail patients.

Conclusion: We present a cohort of patients receiving de-escalated treatment for ASCC. This work quantifies the population, their comorbidities and frailty scores to inform the design of future clinical trials in this underserved population.

Keywords: frailty, co-morbidity, anal cancer

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Digital Poster Phase 1b/II trial of pembrolizumab plus standard radiotherapy with chemotherapy in Squamous Cell Carcinoma of anus (CORINTH): Cohorts safety data Lisette S Nixon 1 , Margherita Carucci 1 , Angela Casbard 1 , Lawrence Raisanen 1 , Catharine Porter 1 , Philip J Markham 1 , Marianne G Guren 2 , Vicky Goh 3 , Thomas Rackley 4 , Samuel Bosompen 5 , Natalie L Abbott 6,7 , Morny Drury 8 , Marcia Hall 9 , Mark Harrison 9 , Richard Adams 1 1 Centre for Trials Research, Cardiff University, Cardiff, United Kingdom. 2 Clinical Oncology, Oslo University Hospital, Oslo, Norway. 3 School of Biomedical Engineering & Imaging Sciences, King’s College London, London, United Kingdom. 4 Clinical Oncology, Velindre University NHS Trust, Oslo, United Kingdom. 5 Pharmacy, Frimley Health NHS Foundation Hospital, Slough, United Kingdom. 6 St. Bartholomews Hospital, Barts Health NHS Trust, London, United Kingdom. 7 RTTQA, Velindre University NHS Trust, Cardiff, United Kingdom. 8 Consumer Representative, The