Platinum, fluorouracil and taxane based regimen are all acceptable in the first line treatment of metastatic gastric cancer. The TX and XELOX regimen are two common regimen used in MGC. whichever regimen is used, the average response rate is less than 50%. So a rather part of patients can't get benefit from the treatment. It is urgent to find out the predictive factors of these regimens in order to get a higher response and better survival outcome.

Patients with MGC will be treated with TX or XELOX regimen. Before treatment, 14 days after treatment and after progression, the blood sample will be collected. Primary tumor blocks will also of collected. These samples will be used to detect predictive factors of the two types first line therapy.

Inclusion Criteria:

• Chemo-naive patients with metastatic, unresectable, histologically confirmed gastric or Gastroesophageal adenocarcinoma; Patients who received adjuvant chemotherapy, the duration from the last therapy to relapse at least longer than 6 months
• Patient must have at least one measurable lesions (RECIST 1.1)
• 18 Years to 75 years
• Written informed consent obtained
• Eastern Cooperative Oncology Group (ECOG) performance status 0-1
• Patients must have adequate organ and marrow function as defined below:
• neutrophilicgranulocyte greater than/equal to 1,500/mm3;
• platelets greater than/equal to 90,000/ mm3;
• hemoglobin greater than/equal to 9 gm/dL (may be transfused to maintain or exceed this level);
• total bilirubin less than/equal to 1.5 within institutional upper limit of normal (IULN);
• Aspartate Transaminase (AST,SGOT)/Alanine transaminase (ALT,SGPT) less than/equal to 2.5 times IULN
• serum creatinine less than/equal to 1.5 x IULN.

Exclusion Criteria:

• Active clinically serious infections (> grade 2 NCI-CTC version 3.0, National Cancer Institute-Common Terminology Criteria for Adverse Events)
• Symptomatic metastatic brain or meningeal tumors
• History of organ allograft
• Patients undergoing renal dialysis
• chronic inflammatory bowel disease; ileus; genetic fructose intolerance
• Patients who received adjuvant chemotherapy and the duration from the last therapy less than 6 months
• Receive previously radiotherapy in measurable regions
• Pregnancy or lactating status
• Concurrent malignancy other than nonmelanoma skin cancer, or in situ cervix carcinoma
• Clinically relevant coronary artery disease or history of a myocardial infarction within the last 12 months
• Acute or subacute intestinal occlusion or history of the inflammatory bowel disease
• Any factors that influence the usage of oral administration