ESTRO 2025 - Abstract Book

S1279

Clinical – Lower GI

ESTRO 2025

References: [1] Shah S et al. RE. Validation of the Neoadjuvant Rectal Cancer (NAR) Score for Prognostication Following Total Neoadjuvant Therapy (TNT) for Locally Advanced Rectal Cancer. J Gastrointest Cancer. 2023 Sep;54(3):829-836 [2] Rosenberg, I.D. et al. (2022). PO-1322 NAR Score validation in TNT (Total Neoadjuvant Treatment) for locally advanced rectal cancer. Radiotherapy and Oncology. 170. S1117. 10.1016/S0167-8140(22)03286-8. [3] Van Griethuysen, J. J. M. et al. (2017). Computational Radiomics System to Decode the Radiographic Phenotype. Cancer Research, 77(21), e104–e107. [4] Pedregosa, F. et al. (2011). Scikit-learn: Machine learning in Python. Journal of Machine Learning Research 2825– 2830.

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Proffered Paper Sex-disparities in anal cancer staging: is vaginal invasion as clinically relevant as invasion into other organs? Shefali P Parikh, Beshar Allos, Ian Geh Clinical Oncology, University Hospitals Birmingham NHS Trust, Birmingham, United Kingdom Purpose/Objective: The TNM T-staging of anal cancer is based on maximal tumour diameter from T1 to T3 disease. T4 tumours invade adjacent organs such as the prostate, penis, or vagina. 1 However, the anogenital distance in females is on average half as long as in males 2,3 , with further reduction after menopause. 4 Thus the risk of vaginal invasion may be disproportionately higher in smaller, less bulky tumours. This study explores whether the prognosis of T4 tumours in female patients is more favourable than expected. Material/Methods: 401 consecutive patients with non-metastatic anal cancer treated with radical chemo-radiotherapy were identified from a prospectively maintained database at a single U.K. tertiary center, from 1999 to June 2022. Follow-up data was censored on 03/01/2024. R studio 2023.09 was used to analyse survival data, and cox-regression analysis used to identify prognostic factors. Results: Data from 132 males and 269 females were analysed. Median age was 63 years. Disease was staged as T4 in 21/132 (16%) males and 73/269 (27%) females, corresponding to a median tumour size of 8cm (IQR 4cm) and 6.5cm (IQR 2.5cm) respectively. 63/73 (86%) females had T4 disease due to vaginal involvement. 3-year overall survival (OS) in men with T1 to T4 disease was a stepwise downward trend - 90%, 86%, 70% and 66% respectively. In contrast, OS in women with T1 to T4 disease was 96%, 91%, 76% and 90% respectively. Similar patterns were seen for 3-year disease free survival (DFS) as represented in Table 1. Thus, the prognosis of T4 cancers in women was intermediate between T2 and T3 disease. On multivariate analysis male sex (HR 1.6, p = 0.02) and anal margin cancers (HR 2.0, p = 0.03) were independently predictive of a worse OS. Age <65 years (HR 0.3, p = 0.0001), tumour size ≤5cm (HR 0.6, p = 0.03) and N0 disease (HR 0.6, p = 0.016) were all independently good prognostic factors. Tumour size and age retained significance as continuous variables. T staging could not be analysed as a prognostic marker due to lack of an ordinal pattern in survival outcomes.