P1.125. Challenging a Histology-Led Paradigm: Comparable Real-World Survival After Definitive Non-Surgical Treatment in Oesophageal Adenocarcinoma and Squamous Cell Carcinoma

Abstract

Abstract Topic Esophageal Cancer: Oncology/Radiation Therapy Background Histology is often treated as a surrogate for radiosensitivity in oesophageal cancer, sustaining the prevailing assumption that squamous cell carcinoma (SCC) benefits more from definitive chemoradiotherapy than adenocarcinoma (AC). We examined whether overall survival (OS) is better discriminated by histology within a fixed pathway, or by the delivered treatment pathway. Methods Retrospective 10-year single-centre regional cohort of oesophageal cancer treated with radical intent. Patients were grouped by delivered pathway: definitive radiotherapy (dRT), definitive chemoradiotherapy (dCRT), or neoadjuvant chemoradiotherapy (nCRT). Histology-stratified analyses compared AC versus SCC within dCRT and within dRT; a separate SCC-only analysis compared nCRT, dCRT and dRT. OS was measured from decision-to-treat to reduce pathway-dependent lead-time, including chemotherapy cycles before radiotherapy in dCRT patients. Kaplan–Meier methods estimated median OS and landmark OS. Comparisons used log-rank tests (primary) and Gehan–Breslow–Wilcoxon tests (early-event weighting). Cox models generated hazard ratios (HR) with 95% confidence intervals; two-sided p<0.05 was significant. Results Among 553 radical-intent patients (dRT n=278, dCRT n=200, nCRT+S n=75), dCRT showed superior OS versus dRT (median 29.0 vs 19.2 months; 5-year OS 30.0% vs 21.2%; 10-year OS 13.4% vs 3.8%; log-rank p=0.0005). nCRT achieved longer OS than dCRT (median 80.2 vs 29.0 months; 5-year OS 56.2% vs 30.0%; 10-year OS 34.1% vs 13.4%; log-rank p=0.0035). Within dCRT, OS was similar for AC (n=96) and SCC (n=97) (median 31.4 vs 27.1 months; 5-year OS 30.2% vs 29.8%; log-rank p=0.702). Within dRT, AC (n=164) and SCC (n=84) did not differ by log-rank (median 21.4 vs 13.8 months; 5-year OS 21.1% vs 13.8%; p=0.146), despite an early difference (Wilcoxon p=0.0127). In SCC, OS differed markedly by pathway: nCRT (n=67) median 95.4 months with 5-year OS 59.0%; dCRT (n=97) median 27.1 months with 5-year OS 29.8%; dRT (n=84) median 13.8 months with 5-year OS 13.8% (global log-rank p<0.0001). Conclusion In this real-world cohort, survival differed primarily by the treatment pathway delivered, not by histology. Within definitive chemoradiotherapy, AC and SCC had comparable OS, challenging the routine assumption that histology alone predicts benefit. In definitive radiotherapy, early differences without sustained separation were consistent with time-dependent selection rather than durable biology. The practical implication is clear: pathway decisions and service delivery that enable combined-modality radical treatment are likely to influence outcomes more than histology-led expectations.