RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die.

PURPOSE: Phase II trial to study the effects of cladribine in previously treated or untreated patients with mantle cell lymphoma.

OBJECTIVES: I. Determine the efficacy of cladribine (2-chlorodeoxyadenosine; 2-CdA) as treatment for mantle cell lymphoma (MCL) either as initial therapy or for relapsed/refractory disease. II. Determine by flow cytometry immunophenotyping of blood lymphocytes the number of patients with peripheral blood involvement at the time of diagnosis and compare the presence or absence of peripheral blood involvement with response data. III. Detect rearrangements involving the bcl-1 gene and immunoglobulin heavy chain locus by molecular techniques (e.g., polymerase chain reaction, Southern blotting, or in situ hybridization), and compare these results with immunohistochemical demonstration of bcl-1 protein expression. VI. Determine the proliferative rate of MCL by immunohistochemistry and DNA content flow cytometry. V. Summarize the toxic effects associated with this treatment.

OUTLINE: Patients receive cladribine (2-chlorodeoxyadenosine; 2-CdA) daily for 5 days every 4 weeks for a maximum of 6 courses; response is assessed after every 2 courses. Patients in complete remission or with stable disease discontinue treatment and are followed; those with disease progression at any time are removed from study. Patients are followed every 2 months for 1 year, every 4 months for 1 year, every 6 months for 1 year, and annually for 2 years.

PROJECTED ACCRUAL: Up to 25 previously treated patients will be entered over approximately 3 years if there is at least 1 response in the first 11 patients. Up to 23 previously untreated patients will be entered over approximately 3 years if there are at least 4 responses in the first 13 patients.

DISEASE CHARACTERISTICS: Histologically confirmed mantle cell lymphoma (MCL) requiring therapy NCCTG pathology review required - Repeat biopsy is required for previously treated patients with previously biopsy proven MCL who relapse after achieving a partial or complete remission - Rebiopsy is not required for patients with: Progression of previously biopsy proven MCL who have not received therapy since the diagnostic biopsy OR Previously biopsy proven MCL who progress or achieve less than a partial remission following initial therapy Measurable or evaluable disease

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-3 Life expectancy: At least 12 weeks Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin normal AST no greater than 3 times normal (5 times normal with liver involvement) Renal: Creatinine no greater than 2.0 mg/dL Cardiovascular: No uncontrolled hypertension No unstable angina No active congestive heart failure No myocardial infarction within 6 months No serious uncontrolled arrhythmia Other: No active or uncontrolled infection No HIV antibody No medical or psychiatric condition that precludes participation No malignancy in the past 5 years, except carcinoma in situ of the cervix, resected basal cell or squamous cell carcinomas of the skin, or prostate cancer that is in remission following a radical retropubic prostatectomy or radiation therapy No pregnant or nursing women Negative pregnancy test required of fertile women within 7 days prior to entry Effective contraception required of fertile patients throughout study and at least 30 days thereafter

PRIOR CONCURRENT THERAPY: Recovered from any reversible acute toxic effects of previous therapy Biologic therapy: Not specified Chemotherapy: At least 4 weeks since chemotherapy (8 weeks since nitrosoureas or mitomycin) No prior fludarabine, pentostatin, or cladribine Endocrine therapy: Not specified Radiotherapy: No prior radiotherapy to greater than 25% of bone marrow Surgery: Not specified