Conversion Therapy Plus Surgery and Radiotherapy for Retroperitoneal Nodal Metastases in Gastric Cancer

"The SOX regimen consists of oxaliplatin 130 mg/m² IV on day 1 plus oral S-1 (tegafur/gimeracil/oteracil) 40-60 mg twice daily, taken on days 1-14 followed by 7 days off, in a 21-day cycle.~Experimental arm: 3 cycles before surgery, 5 cycles after surgery. Control arm: up to 8 cycles as standard systemic therapy."

"The CAPEOX regimen consists of oxaliplatin 130 mg/m² IV on day 1 plus oral capecitabine 1000 mg/m² twice daily on days 1-14, repeated every 3 weeks (q3w), up to 8 cycles.~Used as a standard chemotherapy option in the control arm, with or without PD-1 inhibitor according to PD-L1 CPS score."

"A PD-1 inhibitor is administered intravenously at a fixed dose of 200 mg every 3 weeks.~It is combined with SOX in the experimental arm (CPS ≥1 patients) during conversion and adjuvant phases, and with CAPEOX or SOX in the control arm (CPS ≥1 patients).~Maintenance PD-1 inhibitor continues for up to 1 year or until disease progression or unacceptable toxicity."

"Intensity-modulated radiotherapy (IMRT) is delivered postoperatively to the para-aortic (station 16) nodal basin.~Elective nodal basin: 45-50 Gy in 25 fractions Positive nodes: 56-60 Gy in 25 fractions Radiotherapy is given concurrently with oral capecitabine or S-1 as radiosensitizers."

"During para-aortic IMRT, patients receive concurrent oral capecitabine 825 mg/m² twice daily on radiation days, or oral S-1 dosed according to body surface area.~These agents are used as radiosensitizers during postoperative radiotherapy."