S703
Clinical – Lower GI
ESTRO 2026
pathological CR (pCR). Baseline MRI parameters (T- stage, mesorectal fascia [MRF] status, EMVI) and haematological indices (neutrophils, lymphocytes, platelets, NLR, PLR) were analysed. Logistic regression models assessed univariate and multivariate predictors of CR, with EMVI, sex, age, T-stage, and MRF as covariates. Results: Patient demographics and MRI staging characteristics are shown in Table 1. Overall, 50 patients (27.2%) achieved CR (n=21 cCR, n=29 pCR). 134 (72.8%) patients had an incomplete response.Presence of EMVI, a higher NLR and PLR were significantly associated with a reduced likelihood of achieving a complete response to TNT on univariate and multivariate analysis after adjustment for other clinical variables (Table 2). EMVI showed strong negative association (OR 0.33, p=0.003), as did NLR (OR 0.58, p=0.002). NLR and PLR were highly collinear.This effect was maintained in our largest subgroup, the OPRA-like cohort, where the presence of EMVI (OR 0.25, p=0.01) and a higher NLR (OR 0.57, p=0.02) correlated with a reduced likelihood of CR. The combined NLR + EMVI logistic regression model, adjusted for sex, age, T- stage and MRF status predicted complete response retrospectively, with an AUC of 0.72.
trials is warranted to confirm its tumor response and long-term prognosis. Keywords: non-operative management, complete response
Digital Poster 1925
Baseline haematological and radiological predictors of complete response to total neoadjuvant therapy in locally advanced rectal cancer Zeeshan Arif 1 , Okezie Ucheikonne 2 , Mark P Saunders 1 , Eleanor J Cheadle 3 , Blake Joseph 4 , Bangxiang Guan 2 , Timothy M Illidge 5,1 , Paul A Sutton 6,3 , Claire Arthur 1 1 Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 2 Clinical Outcomes and Data Unit, The Christie NHS Foundation Trust, Manchester, United Kingdom. 3 Division of Cancer Sciences, The University of Manchester, Manchester, United Kingdom. 4 The Grange University Hospital, Aneurin Bevan University Health Trust, Newport, United Kingdom. 5 Faculty of Targeted Therapy and Oncology, The University of Manchester, Manchester, United Kingdom. 6 Colorectal & Peritoneal Oncology Centre, The Christie NHS Foundation Trust, Manchester, United Kingdom Purpose/Objective: Total Neoadjuvant Therapy (TNT) is considered standard of care for mismatch repair proficient, locally advanced rectal adenocarcinoma (LARC). Heterogeneity persists in patient selection, TNT regimen and endpoints, with limited data to inform allocation to a specific treatment approach1. Translational research has explored the tumour immune microenvironment2 yet there are no proven biomarkers of complete response. Neutrophil-to- lymphocyte ratio (NLR) and radiological extramural vascular invasion (EMVI) have previously been shown to correlate with tumour microenvironment and overall survival3,4. This study evaluated whether baseline full blood count (FBC)–derived ratios (NLR and platelet-to-lymphocyte ratio [PLR]) and baseline MRI features could predict complete response (CR) to TNT. Material/Methods: A prospectively maintained database including all patients with stage III LARC who commenced TNT at our institution between December 2020 – December 2024 (n=184) was reviewed. Patients treated with a novel agent as part of a clinical trial were excluded from this analysis. TNT approach reflected contemporary practice: RAPIDO-like (n=55, 30%), consolidation OPRA-like (n=105, 57%), PRODIGE-like (n=11, 6%), and other TNT regimens (n=13, 7%). Complete response (CR) was defined as sustained clinical CR (cCR) six months post-TNT completion or
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