Preoperative Chemoradiotherapy for Locally Advanced Resectable Gastric Adenocarcinoma

Inclusion Criteria: 1. Age ≥ 20 years old 2. Histologically confirmed gastric adenocarcinoma 3. clinical stage : resectable gastric cancer * advanced confirmed (EGD) * extramural infiltration\> 1 mm (CT) * positive serosa invasion (EUS) 4. Eastern Cooperative Oncology Group performance status 0 or 1 5. no prior chemotherapy and radiotherapy 6. measurable lesion or evaluable lesion according to Response Evaluation Criteria in Solid Tumors version 1.1 criteria 7. Patients with adequate organ function 8. Signed informed consent Exclusion Criteria: 1. Metastasis esophageal invasion \> 3cm 2. inoperable peritoneal seeding disease determined by exploratory laparotomy 3. T4b invading the surrounding organs 4. lymph node metastasis outside the celiac trunk Lymph node and splenic lymph node 5. uncontrolled viral infections (HIV, HBV, HCV) 6. Pregnant or lactating women, women of childbearing potential not employing adequate contraception 7. severe hypersensitivity reactions to S-1, cisplatin 8. Subjects with uncontrolled clinically significant cardiovascular medical history, uncontrolled infection or complication 9. Other co-existing malignancies or malignancies diagnosed within the last 5 years except for curatively treated non-melanoma skin cancer or in situ carcinoma of the cervix