Phase II Trial of Neoadjuvant Thymalfasin, PD-1 Inhibitor, and Chemoradiotherapy for cStage III GEJ Adenocarcinoma

This is a prospective, single-center, randomized controlled, phase II clinical trial. The study aims to enroll 48 patients with resectable, locally advanced gastroesophageal junction adenocarcinoma who have not received any treatment. After obtaining informed consent and meeting the inclusion/exclusion criteria, patients were randomly assigned preoperatively in a 1:2 ratio: Arm A. Radiochemoimmunotherapy group (n=16): 3 cycles of serplulimab combined with modified SOX (mSOX) combined with radiotherapy, as details: Cycle 1: Serplulimab: 300 mg, i.v., D1 Oxaliplatin: 130 mg/m², i.v., D1 S-1 (Tegafur/Gimeracil/Oteracil): Oral administration: 40 mg twice daily for BSA \< 1.25 m²; 50 mg twice daily for BSA 1.25 to \<1.5 m²; 60 mg twice daily for BSA ≥ 1.5 m². Administered from D1 to D14, followed by a rest period from D15 to D21. This cycle lasts 21 days. Cycle 2: Serplulimab: 300 mg, i.v., D1 S-1: Oral administration: 40 mg twice daily from D1 to D14 of the treatment cycle. Radiotherapy: Commences between D2 and D5 after the start of Cycle 2. The clinical target volume (CTV) is defined as the endoscopically marked tumor boundary and adjacent metastatic lymph nodes plus a 5-10 mm margin. The planning target volume (PTV) is generated by adding an additional 5-10 mm margin to the CTV. The planned dose to the PTV is 44 Gy administered in 22 fractions, with 5 fractions per week. This is followed by a 7-day rest interval. This cycle lasts 33 days. Cycle 3: Serplulimab: 300 mg, i.v., D1 Oxaliplatin: 130 mg/m², i.v., D1 Fluorouracil Injection: Administered as a 400 mg/m² intravenous bolus on day 1, followed immediately by a continuous intravenous infusion of 2400-3000 mg/m² over 46 hours. This is followed by a 7-day rest period. This cycle lasts 9 days. Arm B: Immunomodulation group (n=32): 3 cycles of serplulimab combined with mSOX combined with radiotherapy (as described above) and 9 weeks of neoadjuvant thymosin; After neoadjuvant therapy, the efficacy of the therapy and the feasibility of radical D2 resection are assessed through imaging examinations. Efficacy evaluation is performed within 2 weeks of the completion of neoadjuvant therapy, and radical gastrectomy is performed within 4-6 weeks. Postoperative treatment is determined jointly by the clinician and the patient based on actual clinical practice. The primary endpoint is complete pathological response (pCR) rate, defined as the proportion of subjects who have no residual surviving tumor cells under microscopic examination and are negative for lymph nodes. Safety assessment: Safety assessments are performed after each cycle of neoadjuvant therapy and 30 days postoperatively. Event follow-up: Follow-up events are then conducted every 3 months for the first year postoperatively, and every 6 months for 1-2 years, up to 2 years postoperatively.