Open label single arm phase II study of Pemetrexed plus Oxaliplatin in patients with advanced gastric carcinoma not previously treated with palliative chemotherapy. 43 Patients will be enrolled in this local trial. The primary objective of this study is to determine the response rate of the treatment.Schedule for this study is as follows: 6 cycles/21 days of Pemetrexed 500 mg/m2 followed by Oxaliplatin 120 mg/m2. This study will also include pharmacogenomic and pharmacogenetic investigations in order to assess determinants of efficacy and toxicity of the treatment with Pemetrexed and Oxaliplatin in the study population.

Inclusion Criteria

• Histologically proven diagnosis of adenocarcinoma of the stomach (including adenocarcinoma of the gastroesophageal junction)
• Stage IIIB or Stage IV disease, according to American Joint Committee on Cancer criteria, not amenable to curative surgery or radiation
• Disease status must be that of at least of one measurable disease as defined by RECIST criteria.
• Performance Status of 2 on the ECOG Scale.
• Adequate organ function including the following:
• Bone marrow: absolute neutrophil count (ANC) >or equal to 1.5 * 109/L, platelets >or equal to 100 *109/L, hemoglobin > or equal to 10 g/dL.
• Hepatic: bilirubin < or equal to 1.5 x ULN; alkaline phosphatase, aspartate transaminase (AST) and alanine transaminase (ALT) < or equal to 3 x ULN (alkaline phosphatase, AST, ALT minor or equal to 5 x ULN is acceptable if liver has tumor involvement), serum albumin > or equal to3g/dL.
• Renal: Calculated creatinine clearance major or equal to 45 ml/min (using the standard Cockcroft-Gault formula).

Exclusion Criteria

• No Prior palliative chemotherapy for advanced disease
• Previous radiation therapy is allowed but should have been limited and must not have included whole pelvis radiation. Patients must have recovered from the toxic effects of the treatment prior to study enrollment (except for alopecia). Prior radiotherapy must be completed at least 30 days before study enrollment
• Known or suspected brain metastasis
• Second primary malignancy (except for in situ carcinoma of the cervix or adequately treated basal cell carcinoma of the skin or other malignancy treated at least 5 years previously with no evidence of recurrence)
• Inability to interrupt aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) 2 days before, the day of, and 2 days after the dose of pemetrexed plus oxaliplatin