Inclusion Criteria

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