Gemcitabine in Treating Patients With Newly Diagnosed, Relapsed, or Chemotherapy-Resistant Mantle Cell Lymphoma

DISEASE CHARACTERISTICS: Histologically confirmed mantle cell lymphoma meeting 1 of the following criteria: Newly diagnosed Chemotherapy resistant Relapsed disease after no more than 2 prior lines of chemotherapy Measurable disease At least 1 unidimensionally measurable lesion ≥ 11 mm by CT scan No prior or current CNS lymphoma or lymphomatous meningosis PATIENT CHARACTERISTICS: Age 18 and over Performance status WHO 0-1 Life expectancy Not specified Hematopoietic Neutrophil count ≥ 1,500/mm^3 (1,000/mm^3 in case of bone marrow infiltration) Platelet count ≥ 100,000/mm^3 (75,000/mm^3 in case of bone marrow infiltration) Hepatic Bilirubin ≤ 2 times upper limit of normal (ULN) Alkaline phosphatase ≤ 2 times ULN AST and ALT ≤ 2 times ULN No active hepatitis Renal Creatinine clearance ≥ 50 mL/min Cardiovascular No congestive heart failure No New York Heart Association class III or IV heart disease No unstable angina pectoris No significant cardiac arrhythmia or arrhythmia requiring chronic treatment No myocardial infarction within the past 3 months Immunologic No active autoimmune disease No ongoing infection (e.g., HIV) Other Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 12 months after study participation No other malignancy within the past 5 years except nonmelanoma skin cancer or adequately treated carcinoma in situ of the cervix No uncontrolled diabetes mellitus No gastric ulcers No other uncontrolled medical condition that would preclude study participation PRIOR CONCURRENT THERAPY: Biologic therapy No concurrent thalidomide Chemotherapy See Disease Characteristics Endocrine therapy Not specified Radiotherapy Prior radiotherapy allowed provided indicator lesions were not in the irradiated field No concurrent radiotherapy to the lungs or mediastinum Surgery Not specified Other More than 30 days since prior systemic anticancer treatment More than 30 days since prior clinical trial participation No other concurrent anticancer drugs No other concurrent experimental drugs