Lapatinib Ditosylate and Capecitabine in Treating Patients With Metastatic Pancreatic Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed metastatic adenocarcinoma of the pancreas * Measurable or non-measurable disease * Measurable disease is defined as ≥ 1 lesion that can be accurately measured in ≥ 1 dimension (longest diameter to be recorded) as ≥ 20 mm with conventional techniques or as ≥ 10 mm with spiral CT scan * No known brain metastases or leptomeningeal disease PATIENT CHARACTERISTICS: * ECOG performance status 0-1 * Life expectancy \> 12 weeks * ANC ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Hemoglobin ≥ 9 g/dL * Albumin ≥ 2.5 g/dL * Serum bilirubin ≤ 1.5 times upper limit of normal (ULN) (2.5 times ULN if Gilbert's syndrome is present) * AST and ALT ≤ 3 times ULN (5 times ULN if documented liver metastases are present) * Creatinine \< 1.5 times ULN * Cardiac ejection fraction normal by ECHO or MUGA scan * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Able to swallow and retain oral medication * No gastrointestinal (GI) tract disease resulting in an inability to take oral medication, malabsorption syndrome, requirement for IV alimentation, or uncontrolled inflammatory GI disease (e.g., Crohn's disease or ulcerative colitis) * No active hepatic or biliary disease, except for Gilbert's syndrome, asymptomatic gallstones, liver metastases, or stable chronic liver disease per investigator assessment * No active cardiac disease within the past 6 months, including any of the following: * Uncontrolled angina * Clinically significant arrhythmia, except for asymptomatic atrial fibrillation requiring anticoagulation * Myocardial infarction * Uncontrolled or symptomatic congestive heart failure * Any other cardiac condition that, in the opinion of the treating physician, would make this study unreasonably hazardous for the patient * No concurrent uncontrolled illness including, but not limited to, ongoing or active infection or psychiatric illness/social situation that would limit compliance with study requirements * No known immediate or delayed hypersensitivity reaction or idiosyncrasy to drugs chemically related to lapatinib ditosylate or any of its excipients, capecitabine, or fluorouracil * No known dihydropyrimidine dehydrogenase (DPD) deficiency * No other malignancy within the past 5 years except for completely resected nonmelanoma skin cancer or successfully treated in situ carcinoma PRIOR CONCURRENT THERAPY: * Recovered from prior radiotherapy or surgery * No prior surgical procedures affecting absorption * No prior EGFR- or ErbB2-targeting therapies * No prior capecitabine * No prior chemotherapy for locally advanced or metastatic pancreatic cancer * At least 3 months since prior adjuvant chemotherapy * Prior fluorouracil allowed as a radiosensitizer only * More than 30 days (or 5 half-lives) since prior investigational drugs * No concurrent radiotherapy or surgery for metastatic cancer * No concurrent combination antiretroviral therapy for HIV-positive patients * No concurrent CYP3A4 inducers or inhibitors * No other concurrent investigational agents or anticancer therapy (e.g., cytotoxic or biologic therapy) * No concurrent herbal (alternative) medicines