Imatinib, Capecitabine, and Cisplatin in Treating Patients With Unresectable or Metastatic Stomach Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed gastric cancer * Unresectable and/or metastatic disease * Incurable with any conventional multimodality approach by interdisciplinary assessment of the local tumor board * Immunohistochemical documentation of c-kit (CD117) and PDGF-R overexpression by tumor if obtainable (preferably on a tumor sample taken within 6 weeks of study entry) * At least one evaluable site of disease according to RECIST criteria * No known brain metastasis or CNS disorder that might alter study compliance or may worsen during or following therapy PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * WBC ≥ 3,000/μL * ANC ≥ 2,000/μL * Platelet count ≥ 100,000/μL * Hemoglobin ≥ 9.0 g/dL * Total bilirubin \< 2 times upper limit of normal (ULN) * SGOT and SGPT \< 2.5 times ULN (5 times ULN if hepatic metastases present) * Glomerular filtration rate ≥ 60 mL/min * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective barrier contraception during and for up to 3 months after completion of study treatment * No known or documented hypersensitivity against fluoropyrimidines, tyrosine kinase inhibitors, cisplatin, other platinums, or their respective derivatives * No gastrointestinal disorder that might affect the gastrointestinal absorption of capecitabine or imatinib mesylate or ability to swallow for the oral administration of capecitabine or imatinib mesylate * At least 5 years since prior primary malignancy except if the other primary malignancy is not currently clinically significant nor requiring active intervention, or if other primary malignancy is a basal cell skin cancer or carcinoma in situ of the cervix * No other concurrent malignant disease * No NYHA class III-IV cardiac disease (i.e., congestive heart failure or myocardial infarction within the past 6 months) * No severe and/or uncontrolled medical disease (i.e., uncontrolled diabetes, chronic renal disease, or active uncontrolled infection) * No known neuropathy, impaired hearing, history of seizures, and/or psychiatric disorder that might alter study compliance or may worsen during or following therapy * No documented dihydropyrimidine dehydrogenase deficiency * No known chronic liver disease (i.e., chronic active hepatitis or cirrhosis) * No known diagnosis of HIV infection or other serious uncontrolled infections * No significant history of non-compliance to medical regimens or inability to grant reliable informed consent PRIOR CONCURRENT THERAPY: * No chemotherapy or investigational agents within the past 4 weeks (6 weeks for nitrosoureas or mitomycin C) unless the disease is rapidly progressing * No prior radiotherapy to ≥ 25% of the bone marrow * No major surgery within the past 2 weeks * No concurrent warfarin or acetaminophen * Therapeutic anticoagulation using heparin or low-molecular weight heparin allowed * No concurrent sorivudine or related substances * No other concurrent anticancer agents, including chemotherapy and biologic agents * No other concurrent investigational drugs