This single-center, open-label, randomized phase II trial (JAGC-1) will evaluate whether adjuvant chemotherapy can be safely omitted in patients with stage IB-III gastric cancer (cT2-4a and/or N+) who have achieved a pathological complete response (pCR) or TRG 4-5 on the Mandard scale, following neoadjuvant chemotherapy and surgery. The study aims to compare disease-free survival and quality of life in patients receiving or not receiving adjuvant chemotherapy after neoadjuvant treatment and surgery.