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