Celecoxib/Oxaliplatin/Capecitabine for Gastric/Gastroesophageal Junction Carcinoma

Inclusion Criteria: * Patient must have histologically proven, pathologically verified and surgically incurable(unresectable, recurrent, or metastatic) gastric/gastroesophageal junction carcinoma. Gastric lymphoma and Gastrointestinal stromal tumor(GIST) are ineligible for this study. At least 6 unstained paraffin-embedded pathologic specimen slides will be required for the COX-2 expression assays. * Patient must have bidimensionally measurable disease as defined below. Measurable lesions must be assessed (by physical examination, CT scan, radionuclide scan or plain X-ray) within 30 days prior to registration. The patient's disease status must be completely assessed and reported. (Measurable Disease: Bidimensionally measurable lesions with clearly defined margins by: 1) Ruler measurement or medical photograph (skin or oral lesion), or plain x ray with at least one diameter .5 cm or greater (bone lesions are not included) or, 2) CT, MRI or other imaging scan with both diameters greater than the distance between cuts of the imaging study, or 3) palpation with both diameters 2 cm or greater.) * All patients must undergo a CT of abdomen and chest within 30 days prior to registration. * Patients may have received prior radiation therapy. Radiation therapy must have been completed at least 30 days before registration. * Patients may have received prior surgery. Prior surgery must have been completed at least 30 days before registration. * Performance status must be 0-2 according to Southwest Oncology Group Criteria Exclusion criteria: * Patients with brain metastases are NOT eligible for this study. It is not mandatory to obtain brain CT or MRI on all patients. However, patients who exhibit neurological symptoms or have pulmonary metastases on radiographic studies must obtain brain CT w/ IV contrast or MRI prior to registration to ascertain the presence of brain metastasis. * Patients must NOT have received capecitabine or oxaliplatin. Prior use of cisplatin, carboplatin, 5-FU are permitted. Prior systemic therapy must have been completed at least 30 days before registration. * Pregnant or nursing women are not eligible to participate in this trial because the safe use of these drugs in pregnancy have not been established. Urine pregnancy test must be done prior to the study. * Patient must NOT have known allergic reaction to sulfonamides * Patient must NOT have known allergic or other adverse reaction to celecoxib * Patient must NOT have persistent peripheral neuropathy * Patient must NOT have known hypersensitivity reactions to 5-FU or platinum * Patient must NOT have active gastric/duodenal bleeding * Patient must NOT have had a sensitivity reaction to aspirin or other NSAIDS nonsteroidal antiinflammatory drugs (NSAIDS) \[experiencing asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs\]