Gemcitabine and Imatinib Mesylate as First-Line Therapy in Patients With Locally Adv. or Metastatic Pancreatic Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed pancreatic adenocarcinoma or poorly differentiated carcinoma (originating in the pancreas) * Locally advanced or metastatic disease * Not eligible for curative resection * Must have measurable or evaluable disease as defined by RECIST criteria * No CA19-9 elevation as only evidence of disease * No known brain metastases PATIENT CHARACTERISTICS: * ECOG performance status 0-2 * Absolute neutrophil count ≥ 1,500/mm³ * Platelet count ≥ 125,000/mm³ * Bilirubin \< 1.5 times upper limit of normal (ULN) * AST and ALT ≤ 2.5 times ULN * Alkaline phosphatase \< 3 times ULN * Creatinine ≤ 1.5 times ULN OR creatinine clearance ≥ 60 mL/min * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective nonhormonal contraception * No coexisting medical condition that would preclude study compliance * No inability to ingest tablets * No active illness (e.g., active or uncontrolled infection, uncontrolled cardiac disease) that would preclude study participation * No chronic uncontrolled diarrhea and/or daily emesis * No other cancer within the past 5 years except for surgically removed noninvasive nonmelanoma skin cancer or in situ cervical cancer PRIOR CONCURRENT THERAPY: * No prior chemotherapy for metastatic disease * No prior gemcitabine * No prior imatinib mesylate * Prior surgical resection and adjuvant fluorouracil chemotherapy allowed provided there was an interval of \> 6 months between the last dose of adjuvant chemotherapy and recurrence of pancreatic cancer * Prior fluorouracil as a radiosensitizing agent allowed * At least 4 weeks since prior radiotherapy and recovered * Must have evidence of disease outside the radiation fields OR radiologically confirmed disease progression within the radiation fields after completion of radiotherapy * No concurrent therapeutic warfarin * Prophylactic warfarin ≤ 1 mg daily allowed for prophylaxis of central venous catheter thrombosis * Low molecular weight heparin or heparin allowed for anticoagulation * No concurrent chronic systemic corticosteroids * No other concurrent agents or therapies, including chemotherapy, immunotherapy, hormonal cancer therapy, radiotherapy, or cancer surgery * No other concurrent experimental medications * No concurrent filgrastim (G-CSF) or sargramostim (GM-CSF)