Hypofractionated Radiotherapy Plus Immunochemotherapy for Neoadjuvant Treatment of Gastroesophageal Junction Adenocarcinoma

In Phase Ib, hypofractionated radiotherapy (HFRT) will be administered at one of three dose levels: 3 Gy × 5 fractions, 4 Gy × 5 fractions, or 5 Gy × 5 fractions. The recommended dose determined in Phase Ib will be used in Phase II (delivered as 5 fractions).

Serplulimab will be administered concurrently with chemotherapy at a fixed dose of 300 mg via intravenous infusion on Day 1 of each 3-week cycle.

The TS regimen includes paclitaxel at a dose of 175 mg/m² administered via intravenous infusion on Day 1, and oral administration of tegafur-gimeracil-oteracil (S-1) for 14 consecutive days followed by a 7-day rest period (21-day cycle). The S-1 dose is based on body surface area (BSA): 40 mg twice daily (bid) for BSA ≤ 1.5 m²; 50 mg bid for BSA 1.5-1.6 m²; and 60 mg bid for BSA ≥ 1.6 m².