This is an international multi-center trial that will enroll patients with locally advanced, unresectable, or metastatic gastric, esophageal, or gastro-esophageal junction cancer whose tumors have amplification of the ErbB2 (HER2) gene. The trial will investigate whether lapatinib, when added to the chemotherapy regimen, capecitabine plus oxaliplatin (CapeOx), extends the time to progression and overall survival. Tumor ErbB2 (HER2) status must be known before trial entry. CapeOx is administered to all patients, and patients will be randomly assigned to receive either lapatinib or placebo.

• ErbB2 (HER2) Amplified Gastric
• Esophageal
• or Gastro-esophageal Junction Adenocarcinoma That is Unresectable Due to Locally Advanced Metastatic, or Locally Recurrent Disease.

Inclusion Criteria:

Signed informed consent; Histologically confirmed gastric, esophageal, or gastro-esophageal junction adenocarcinoma; disease that is unresectable due to locally advanced, metastatic, or locally recurrent disease; Measurable or non-measurable, but radiologically evaluable disease, according to RECIST; ErbB2 (HER2)positive; Age =18 years; ECOG Performance status = 2; Adequate organ function, including adequate hematologic, renal and liver function; Cardiac ejection fraction within institutional range of normal as measured by echocardiogram; Able to swallow and retain oral medications, and/or receive enteral medications via gastrectomy feeding tube; Women and men with potential to have children must be willing to practice acceptable methods of birth control during the study; Prior gastric surgery is permitted if > 3 weeks prior and recovered; Prior chemotherapy for non-gastric malignancy if > than 5 years; Prior neoadjuvant and/or adjuvant chemotherapy for early stage gastric cancer if > 6 months since completion; At least 4 weeks since prior radiotherapy; Prior biologic, hormonal, or immunologic cancer treatment if > 5 years since treatment.

Exclusion Criteria:

Pregnant or lactating females; Known history of active CNS disease; Uncontrolled ascites; Concurrent anti-cancer therapy; Gastric carcinoid, epidermoid, sarcomas, or squamous cell carcinoma; Prior palliative chemotherapy for the treatment of gastric cancer; Prior treatment with oxaliplatin or the regimen CapeOx; Malabsorption syndrome or uncontrolled inflammatory gastrointestinal disease; Known history of uncontrolled or symptomatic angina, arrhythmias, or congestive heart failure; Pre-existing grade = 2 motor or sensory neuropathy; Uncontrolled infection; Concurrent disease or condition that would make the subject inappropriate for study participation or any serious medical condition that would interfere with the subject''s safety; Active hepatic or biliary disease; History of other malignancy except if disease-free for 5 years, a history of completely resected non-melanoma skin cancer, or a successfully treated in situ carcinoma; Unresolved or unstable serious toxicity from prior administration of another investigational drug and/or prior cancer treatment; Dementia, altered mental status, or any psychiatric condition that would prohibit the understanding or rendering of informed consent; Known history of DPD deficiency; Known immediate or delayed hypersensitivity reaction or idiosyncrasy to drugs chemically related to lapatinib, capecitabine, fluorouracil, platins or their excipients; Use of any investigational drug within 30 days prior randomization; Use of concurrent prohibited medications that would interact with study medications