Oxaliplatin and S-1 or Oxaliplatin and Capecitabine in Treating Patients With Recurrent, Metastatic, or Unresectable Gastric Cancer

DISEASE CHARACTERISTICS:

* Histologically confirmed adenocarcinoma of the stomach
* Unresectable advanced disease or recurrent disease after resection
* At least one radiographically documented (CT scan or MRI) measurable or evaluable lesion in a previously non-irradiated area according to RECIST
* No clinical evidence of brain metastases or history of other CNS disease unless adequately treated

PATIENT CHARACTERISTICS:

* ECOG performance status 0-2
* Estimated life expectancy \> 3 months
* Hemoglobin ≥ 9 g/dL
* White blood cell ≥ 4,000/µL
* ANC ≥ 2,000/µL
* Platelets ≥ 100,000/µL
* Bilirubin ≤ 1.25 times upper limit of normal (ULN) (≤ 2.0 times ULN if hepatic metastasis present)
* Serum creatinine ≤ 1.5 times ULN
* Creatinine clearance ≥ 60 mL/min
* AST/ALT ≤ 3.0 times ULN (≤ 5.0 times ULN if hepatic metastasis present)
* Alkaline phosphatase ≤ 3.0 times ULN (≤ 5.0 times ULN if bone metastasis present)
* Must have an intact gastrointestinal tract
* Able to take oral medications
* No medically uncontrolled severe infections or complications
* No prior malignancy other than gastric cancer in the last 5 years except for basal cell cancer of the skin or preinvasive cancer of the cervix
* Not pregnant or nursing
* No neuropathy ≥ grade 2
* No clinically relevant heart disease
* No evidence of past medical history or psychosocial dysfunction that contraindicates the use of an investigational drug or puts the patient at risk
* No dementia, altered mental status, or any psychiatric condition that would prohibit the understanding or rendering of informed consent
* No uncontrolled hepatitis B or C, chronic liver disease, or diabetes mellitus
* No other evidence of inappropriate suspicious condition

PRIOR CONCURRENT THERAPY:

* No prior chemotherapy for advanced or recurrent disease

  * Prior adjuvant chemotherapy allowed if finished \> 6 months before start of study treatment
* No prior therapeutic radiotherapy

  * Prior palliative radiotherapy allowed if it was not done for primary, evaluable, or intraabdominal lesions
* No prior capecitabine or oxaliplatin
* No other concurrent chemotherapy or radiotherapy (except localized radiotherapy for pain relief)
* No concurrent chemically related analogues, such as warfarin, phenytoin, or allopurinol
* No concurrent steroid therapy except as follows:

  * Prophylactic use for hypersensitivity control or antiemetic purpose allowed
  * Chronic low dose of steroid (less than methylprednisolone 20 mg or equivalent dose) allowed