ESTRO 2025 - Abstract Book

S1209

Clinical – Lower GI

ESTRO 2025

2486

Digital Poster Long-Term Analysis of Chemoradiotherapy in anal cancer: from predictive factors to survival outcomes and toxicities – a single-institution analysis Catarina Moreira van der Elzen, Fátima Aires, Catarina Dias, Margarida Marques, Lígia Osório Radiotherapy, Unidade Local de Saúde de São João, Porto, Portugal Purpose/Objective: Squamous cell carcinoma of the anus(SCCA) is a rare neoplasm. Rising incidence has been reported with coinfection HIV-HPV predisposing it’s development. Current standard-of-care treatment, for locally advanced stages, prioritizes chemoradiotherapy(CRT), but patients may respond differently. Identifying reliable biomarkers able to predict oncological outcomes could help in the development of risk adapted treatment strategies. This study aims to evaluate the role of inflammatory markers as prognostic and predictive factors along with tumour markers and treatment toxicities seeking understanding to a greater risk of treatment failure. Material/Methods: Patients diagnosed with locally advanced non-metastatic SCCA from January/2008 to August/2023, in our institution, were retrospectively collected. Patients underwent radical RT(> 50 Gy) with or without concomitant CT based on mitomycin C±fluoropyrimidines/capecitabine. A pre and post-treatment blood sample was retrieved including SCC(squamous cell carcinoma), CEA(carcinoembryonic antigen), CA19.9(carbohydrate antigen 19.9), Hg(haemoglobin), NLR(neutrophil-to-lymphocyte ratio) and virology status(HIV/HPV). Outcomes of interest were overall survival(OS), local recurrence(LR) and metastasis free survival(MFS). Toxicities classified according to CTCAE criteria(v6). Results: Sixty-five patients were analyzed. Median age 62 years(± 13.2; 32-90), mostly female(64.6%), 92.3% presenting ECOG PS 0-1.Five patients were clinical stage I; 32 stage II and 28 stage III; 14 HPV+; 14 HIV+.Fifty-six received concomitant CT(5-fluorouracil (5-FU)(2);5-FU+Mitomycin(48);Capecitabine(6)).Skin toxicity was the most common acute toxicity(70.4%, G2-3); 9 patients(13.8%) experienced hematologic toxicity,(G1-2 citopenias); 4.8% presented gastrointestinal G3-4 toxicity and 54% genitourinary G1-2 toxicity. Using IMRT demonstrated lower severe toxicity (P=.038 ). Three year OS, LR and MFS was 66.5%, 80.3% and 85.7%, respectively. HIV's presence was associated with lower complete response to treatment (P=.04). Univariate analysis identified that SCC cut-off value >1,3 and NRL cut > 6,86 could predict LR (P=.009;P<.001 ) with NRL also impacting OS (P=.014) and MFS (P<.001). An independent predictor of OS was shown by haemoglobin values(<=11.7g/dL) that were significantly associated with OS(Fig1.) on both univariate (P=.003) and multivariate (P=.005) analysis(Table1.).