A Phase Ib/II Study of Efficacy and Feasibility of Cytoreductive Surgery, Extensive Peritoneal Lavage, Hyperthermicintraperitoneal Chemotherapy and Post-operative Intraperitoneal Chemotherapy Combination in Gastric Cancer With Peritoneal Metastasis

Inclusion Criteria: 1. Patient age of 19 years or older and age of 75 years or younger. 2. Histologically proven gastric or esophagogastric junction adenocarcinoma with peritoneal metastasis under diagnostic laparoscopy. 3. Primary tumor measured as resectable in preoperative images. 4. Performance status based on ECOG : 0\~1 5. No prior treatment (chemotherapy, radiotherapy, etc.) 6. Adequate hepatic, renal, and hematologic function * ANC≥1,500/uL, * hemoglobin≥9.0g/dL * platelet≥100,000/uL * total Bilirubin: ≤ 1.5 × upper normal limit * Creatinine\<1.5mg/dL * AST/ALT, ALP ≤ 2.5 x upper normal limit 7. Patients who can understand this study and sign the consent form. Exclusion Criteria: 1. Patient who has distant metastasis or para-aortic lymph node metastasis or retroperitoneal metastasis except peritoneal metastasis. (But the patient who has ovarian metastasis with resectable status can be enrolled.) 2. Primary tumor cannot be resected because of direct invasion to other important organ. (But, if the invaded organ can be resected together, such as spleen, gallbladder, distal pancreas, and liver, the patient can be enrolled) 3. HER2 positive patient 4. Patient with active viral infection (for example, HIV, HBV, HCV, except stable status of HBV infection) 5. Pregnant patient, or patient in breast-feeding, or who is planning pregnancy. 6. Patients in exclusion criteria of TS-1, cisplatin, paclitaxel * Patients with a history of severe hypersensitivity to these drugs * Patients with severe bone marrow depression * patients who has severe hepatic, renal disorder * patients who has hereditary problem or galactose intolerance, lapp lactase deficiency, or glucose-galactose malabsorption 7. Patients who has important medical problem or infection * Cerebrovascular accident(CVA) within 1 year * Heart attack within 6 months, uncontrolled hypertension, unstable angina, uncontrolled congestive heart failure(CHF), severe arrhythmia * Major operation or injury within 28 days * Severe and not recovered wound, ulcer, fracture * Uncontrolled bleeding disease * Recent active gastric infection 8. Patient with another primary cancer within last 5 years 9. Patient on medication which can interact with the drugs used in this study (fluoropyrimidine-group antineoplastic agents, flucytosine, phenytoin, etc) 10. Patients with other systemic chemotherapy or radiotherapy 11. Patients with psychiatric or neurologic disorder so that he or she cannot understand and sign the consent form.