ESTRO 2025 - Abstract Book

S1239

Clinical – Lower GI

ESTRO 2025

Material/Methods: Retrospective data were collected for patients receiving radical treatment at a regional cancer centre from 2012 2022. Patient and tumour characteristics were assessed, along with treatment - chemoradiation (CRT) vs Radiotherapy alone (RT) (where chemotherapy was contraindicated). Toxicity rates, including incidence of venous thromboembolism (VTE) and outcome data, including tumour recurrence, were compared between age and treatment groups. Results: Among 193 patients, the median age was 63 years and 70% were women. 141 patients (73%) were under 70 years at diagnosis and most patients were treated with chemoradiation (n=172, 89%). At the time of data collection, 137 patients (71%) had a sustained complete response to treatment whilst 48 patients (25%) had recurrence of their anal cancer (median time to recurrence 14m, range 4-48m) and 8 patients (4%) had an incomplete response to treatment. 31 patients (22%) under 70 years, had recurrence compared with 17 (33%) patients over 70. 52 (27%) patients experienced Grade 3 treatment-related toxicity and 45 (23%) had a treatment-related admission. Of patients under 70 years, 40 (28%) patients experienced Grade 3 toxicity and 35 (25%) had treatment related admission. 12 patients (23%) over 70 years (n=52) experienced Grade 3 toxicity and 10 (19%) treatment related admission. Response and recurrence rates were compared between those treated with RT and CRT. 44 patients (26%) in the CRT group had recurrence or had an incomplete response to treatment, compared with 10 (48%) in the RT group. 4 patients (2%) developed VTE within 6 months of their treatment. All patients in this group had a locally advanced tumour (T3 or 4) and 2 had node-positive disease. Conclusion: This study demonstrates treatment response and recurrence rates comparable to published data and equivalent acute severe toxicity between age groups. This demonstrates equivalent tolerability in those over 70 years. Patients in the RT and over 70 years group had apparent higher recurrence rates. The authors acknowledge the potential dissimilar demographics and physical health of these groups, which undoubtedly impact outcomes. Rates of VTE were not high in this group but more work is required to delineate those at highest risk and potentially direct therapy.

Keywords: Anal cancer, audit, radiotherapy

3400

Mini-Oral The prognostic value of circulating cell-free DNA dynamics during chemoradiotherapy in squamous cell carcinomas of the anus Anne V Jakobsen 1,2 , Camilla Kronborg 3,2 , Anne Ramlov 4 , Christian A Hvid 4 , Karen-Lise G Spindler 1,2 1 Department of Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark. 2 Department of Clinical Medicine, Aarhus University, Aarhus, Denmark. 3 The Danish Center for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 4 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark Purpose/Objective: In squamous cell carcinomas of the anus (SCCA), tools for upfront patient selection to individualise treatment are lacking. Liquid biopsies assessing total cell free DNA (cfDNA) provide a minimally invasive approach to track tumor dynamics during treatment. Studies from SCCA and rectal cancer demonstrated that cfDNA can be quantified using a rapid, cost-effective direct fluorescent assay (DFA), but the clinical utility is not established 1,2 . This study investigates the prognostic value of cfDNA dynamics during chemoradiotherapy (CRT) in SCCA.