P1.150. Patterns of Microscopic Longitudinal Extension in Oesophageal Squamous Cell Carcinoma Treated With or Without Neoadjuvant Immunochemotherapy

Topic Esophageal Cancer: Other Background The extent of microscopic tumour spread beyond the gross margin is a key determinant of safe resection margins in oesophageal squamous cell carcinoma (ESCC). Whether neoadjuvant immunochemotherapy modifies patterns of microscopic longitudinal extension remains unclear. Methods Between May and August 2025, we prospectively enrolled 20 patients with c/ycT2–3 oesophageal squamous cell carcinoma (ESCC) who underwent upfront surgery or surgery following neoadjuvant immunochemotherapy. Patients with multiple lesions were excluded. Longitudinally sectioned oesophageal specimens were collected and analysed using haematoxylin and eosin staining. Microscopic longitudinal extension beyond the gross tumour margin was assessed in both proximal and distal directions, distinguishing continuous microscopic extension from discontinuous microscopic spread. Results Thirteen patients underwent upfront surgery and seven received neoadjuvant immunochemotherapy. R0 resection was achieved in all cases. Continuous microscopic extension was identified proximally in 14 patients, and distally in 11 patients. The length of proximal continuous microscopic extension was 0.7 ± 0.5 mm in the neoadjuvant immunochemotherapy group and 3.5 ± 3.9 mm in the upfront surgery group (P=0.086). Distally continuous microscopic extension was 1.3 ± 0.6 mm and 2.8 ± 2.5 mm (P=0.117), respectively. Discontinuous microscopic tumour spread was identified in 7 patients (35%), with a maximum inter-lesional distance of 8.0 ± 9.0 mm. Conclusion Continuous microscopic extension was typically confined within 1 cm, and discontinuous microscopic spread extended up to 3 cm from the primary lesion. Tumours treated with neoadjuvant immunochemotherapy demonstrated a trend towards shorter microscopic extension distances compared with upfront surgery. These findings provide pathological support for individualised consideration of longitudinal resection margins, particularly in anatomically constrained tumours such as cervical/upper oesophageal cancer. A validation study with a larger sample size is currently underway.