Gemcitabine With or Without Dalteparin in Treating Patients With Unresectable or Metastatic Pancreatic Cancer

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed pancreatic adenocarcinoma or poorly differentiated carcinoma of the pancreas that is considered ineligible for curative resection PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Eastern Cooperative Oncology Group 0-2 Life expectancy: Not specified Hematopoietic: White Blood Cell count greater than 3,500/mm^3 Platelet count greater than 100,000/mm^3 No clinically significant bleeding disorder No prior heparin-induced thrombocytopenia Hepatic: Bilirubin less than 2.0 mg/dL aspartate aminotransferase less than 3 times normal Renal: Creatinine less than 2.0 mg/dL Cardiovascular: No prior hemorrhagic stroke No uncontrolled hypertension (sustained blood pressure greater than 200 mm Hg systolic or 110 mm Hg diastolic) Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No other active malignancy No gastrointestinal bleeding within the past 30 days No contraindications to anticoagulation PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy for metastatic disease Prior adjuvant chemotherapy allowed Endocrine therapy: Not specified Radiotherapy: At least 4 weeks since prior radiotherapy and recovered Surgery: Prior surgical resection allowed At least 4 weeks since prior surgery with non-curative intent and recovered More than 30 days since prior neurologic or ophthalmologic surgery Other: At least 2 weeks since prior low-molecular-weight heparin More than 30 days since prior experimental therapeutic agent No concurrent heparin or warfarin for pre-existing condition