Epirubicin Hydrochloride, Cisplatin, and Fluorouracil or Capecitabine With or Without Lapatinib Ditosylate as First-Line Therapy in Treating Patients With Stomach Cancer or Gastroesophageal Junction Cancer

DISEASE CHARACTERISTICS:

* Histologically confirmed adenocarcinoma of the stomach or the esophagogastric junction

  * Metastatic disease OR not amenable to curative surgery
* Tissue material for HER2 and EGFR assessment must be available
* Positive HER2 status by immunohistochemistry (IHC) OR positive EGFR by either fluorescence in situ hybridization (FISH) or IHC at time of randomization
* No clinical signs of CNS involvement

PATIENT CHARACTERISTICS:

* WHO performance status 0-1
* WBC \> 3 x 10\^9/L
* Absolute neutrophil count \> 1.5 x 10\^9/L
* Platelet count \> 100 x 10\^9/L
* Hemoglobin \> 9 g/dL
* Bilirubin ≤ 1.5 times upper limit of normal (ULN)
* AST/ALT ≤ 3 times ULN (≤ 5 times ULN in case of liver metastases)
* Serum creatinine ≤ 2.0 mg/dL
* Creatinine clearance ≥ 60 mL/min
* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective contraception during and for 1 month after completion of study therapy
* LVEF normal by MUGA scan or ECHO
* No serious cardiac illness within the past 6 months
* No previous or concurrent malignancies except for adequately treated cone-biopsied carcinoma in situ of the cervix or basal cell carcinoma of the skin
* Able to swallow and retain oral medication
* No history or evidence of interstitial pneumonitis or pulmonary fibrosis
* No uncontrolled infections or serious illnesses, malabsorption syndrome, or medical conditions including chronic alcohol abuse, hepatitis, HIV, and/or cirrhosis
* No psychological, familial, sociological, or geographical condition potentially hampering compliance with the study protocol or follow-up schedule

PRIOR CONCURRENT THERAPY:

* At least 12 months since prior neoadjuvant or adjuvant chemotherapy
* No other investigational drugs from 28 days prior to the first dose of study treatment until 30 days after the last dose of study treatment
* At least 30 days since prior and no concurrent drugs or herbal constituents known to be inducers or inhibitors of CYP3A4
* No prior palliative systemic chemotherapy
* No prior EGFR pathway-targeting therapy (e.g., antibodies or tyrosine kinase inhibitors)
* No concurrent traditional Chinese medicines
* No concurrent non-drug therapies such as radiotherapy (other than for pain relief) or surgery
* No other concurrent anticancer therapy or investigational agents
* No concurrent grapefruit or its juice