S-1 and Irinotecan Combination Chemotherapy for Advanced Gastric Cancer

Inclusion Criteria: * Pathologically proven unresectable adenocarcinoma of stomach * With uni-dimensionally measurable disease (at least longest diameter 2 cm on conventional CT scan, x-ray or physical examination, or 1cm on spiral CT scan) * Age 18 to 70 years old * Estimated life expectancy of more than 3 months * ECOG performance status of 2 or lower * Adequate bone marrow function(absolute neutrophil count \[ANC\] ≥1,500/µL, hemoglobin ≥9.0 g/dL,and platelets ≥100,000/µL) * Adequate kidney function (serum creatinine \< 1.5 mg/dL) * Adequate liver function (serum total bilirubin \< 2 times the upper normal limit (UNL); serum transaminases levels \<3 times \[\<5 times for patients with liver metastasis\] UNL) * No prior chemotherapy but prior adjuvant chemotherapy finished at least 6 months before enrollment was allowed. (but, prior adjuvant chemotherapy with capecitabine or S-1 or camptothecin analogues was excluded) * No prior radiation therapy for at least 4 weeks before enrollment in the study Exclusion Criteria: * Other tumor type than adenocarcinoma * Central nervous system (CNS) metastases or prior radiation for CNS metastases * Gastric outlet obstruction or intestinal obstruction * Evidence of gastrointestinal bleeding * The patient has bony lesions as the sole evaluable disease. * Past or concurrent history of neoplasm other than stomach cancer, except for curatively treated non-melanoma skin cancer or in situ carcinoma of the cervix uteri * Pregnant or lactating women, women of childbearing potential not employing adequate contraception * Other serious illness or medical conditions * Unstable cardiac disease despite treatment, myocardial infarction within 6 months prior to study entry * History of significant neurologic or psychiatric disorders including dementia or seizures * Active uncontrolled infection * Other serious underlying medical conditions which could impair the ability of the patient to participate in the study * Concomitant administration of any other experimental drug under investigation, or concomitant chemotherapy, hormonal therapy, or immunotherapy * concomitant drug medication; The following drugs cause drug interaction with S-1. i. Warfarin, phenprocoumon: increase bleeding tendency ii. Increase blood concentration of phenytoin iii. sorivudine: inhibit DPD -\> increase toxicity according to fluoropyrimidine iv. allopurinol : decrease activity of S-1