Gemcitabine With or Without Dalteparin in Treating Patients With Locally Advanced or Metastatic Pancreatic Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed metastatic or locally advanced adenocarcinoma of the pancreas * Patients with clinical 'high probability' of pancreatic cancer and biopsy suggestive but not diagnostic of pancreatic cancer may be eligible based on review by the principal investigator * Measurable or evaluable disease * No clinical evidence of active venous thromboembolism PATIENT CHARACTERISTICS: * Karnofsky performance status (PS) 60-100% OR WHO PS 0-2 * Life expectancy \> 12 weeks * Absolute neutrophil count \> 2,000/mm³ * WBC \> 3,000/mm³ * Platelet count \> 100,000/mm³ * Creatinine clearance \> 50 mL/min * INR ≤ 1.5 times upper limit of normal (ULN) * Bilirubin \< 1.5 times ULN (stent allowed) * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * No cerebrovascular accident within the past 6 months * No obvious contraindication to anticoagulation, including the following: * Bleeding diathesis * Active peptic ulcer * Ulcerating cancer into duodenum * No history of other advanced malignancy * No gross hematuria * No melaena or gross evidence of gastrointestinal bleeding (other than piles) * No requirement for a central line * No other significant medial or psychiatric illness that, in the opinion of the investigator, would preclude study participation PRIOR CONCURRENT THERAPY: * No prior gemcitabine hydrochloride-containing treatment * No other concurrent cytotoxic chemotherapy, immunotherapy, hormonal therapy (excluding contraceptives and replacement steroids), or experimental medications * No other concurrent specific anticancer therapy as a result of disease progression * No concurrent caval filter device * No other concurrent anticoagulants for venous thromboembolism or other reasons (e.g., atrial fibrillation) * No concurrent acetylsalicylic acid (\> 75 mg) as an antiplatelet drug for a preexisting cardiovascular condition * No concurrent clopidogrel bisulfate