Randomized phase II study designed to evaluate the efficacy and safety of continuous S-1 plus oxaliplatin versus intermittent S-1 plus oxaliplatin as first-line therapy in patients with recurrent and/or metastastic gastric carcinoma. Within 2 weeks of the end of induction chemotherapy of 6 cycles with S-1 plus oxalipatin, patients who don't experience progression will be randomized to the continuous S-1 plus oxaliplatin arm or the intermittent S-1 plus oxaliplatin arm in a 1:1 ratio.

Inclusion Criteria:

1. Histologically or cytologically confirmed gastric adenocarcinoma with recurrent and/or metastatic disease
2. Age ≥ 18 years
3. Eastern Cooperative Oncology Group (ECOG) performance status 0-2
4. Measurable disease as defined by the Response Evaluation Criteria in Solid Tumors (RECIST) or non-measurable evaluable
5. No prior treatment for recurrent and/or metastatic disease (prior adjuvant/neoadjuvant therapy is allowed if at least 6 months has elapsed between completion of adjuvant/neoadjuvant therapy and enrolment into the study; prior oxaliplatin is not allowed)
6. Adequate major organ function including the following: Hematopoietic function: ANC >= 1,500/mm3, Platelet >= 100,000/mm3, Hepatic function: serum bilirubin =< 1.5 x ULN, AST/ALT levels =< 2.5 x ULN (=< 5 x ULN if liver metastases are present)Renal function: serum creatinine =< 1.5 x ULN
7. Patients should sign a written informed consent before study entry

Exclusion Criteria:

1. Lack of physical integrity of the upper gastrointestinal tract or malabsorption syndrome (e.g. patients with partial or total gastrectomy can enter the study, but not those with a jejunostomy probe), or inability to take oral medication

2. Patients with active (significant or uncontrolled) gastrointestinal bleeding

3. Residual relevant toxicity resulting from previous therapy (with the exception of alopecia) ≥ grade 2 NCI-CTCAE version 3.0

4. Prior and/or current history of peripheral neuropathy

   • grade 1 NCI-CTCAE version 3.0

5. Inadequate cardiovascular function:New York Heart Association class III or IV heart diseaseUnstable angina or myocardial infarction within the past 6 monthsHistory of significant ventricular arrhythmia requiring medication with antiarrhythmics or significant conduction system abnormality

6. Serious concurrent infection or nonmalignant illness that is uncontrolled or whose control may be jeopardized by complications of study therapy

7. Other malignancy within the past 3 years except non-melanomatous skin cancer or carcinoma in situ of the cervix

8. History of or current brain metastases

9. Psychiatric disorder that would preclude compliance

10. Females with a positive or no pregnancy test (within 7 days before treatment start) until childbearing potential can be otherwise excluded (postmenopausal i.e. amenorrheic for at least 2 years, hysterectomy or oophorectomy)

11. Subjects with reproductive potential not willing to use an effective method of contraception

12. Lactating women

13. Known dihydropyrimidine dehydrogenase deficiency

14. Patients receiving a concomitant treatment with drugs interacting with S-1 such as flucytosine, phenytoin, or warfarin et al.

15. Major surgery within 4 weeks of start of study treatment, without complete recovery

16. Radiotherapy within 4 weeks of start of study treatment; 2 weeks interval allowed if palliative radiotherapy was given to bone metastatic site and patient recovered from any acute toxicity