Rituximab and Cladribine in Treating Patients With Newly Diagnosed Non-Hodgkin's Lymphoma

DISEASE CHARACTERISTICS: * Histologically confirmed mantle cell lymphoma\* * Measurable or assessable disease defined as at least one of the following: * Lymph node or tumor mass that is 2.0 cm or more in at least one dimension by CT scan, MRI, or plain radiograph imaging OR greater than 1.5 cm in at least one dimension by physical exam * Splenic enlargement, if the spleen is palpable, at least 3 cm below the left costal margin * Diffuse infiltration of an organ such as the stomach, bone marrow, peripheral blood, liver, lungs, or bowel by lymphoma without a discrete mass would constitute assessable, but not measurable, disease * No known CNS involvement NOTE: \*If tumor tissue is unavailable for biopsy, blood or bone marrow specimens may be used to establish patient eligibility provided fusion signals indicate the presence of t(11;14)(q13;q32) by fluorescence in situ hybridization using CCND1/IGH AND mantle cell lymphoma involvement is determined by morphology 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/mm\^3 * Platelet count at least 100,000/mm\^3 Hepatic * Total or direct bilirubin no greater than upper limit of normal (ULN) (with or without secondary liver involvement) * SGOT no greater than 3 times ULN (5 times ULN if there is liver involvement) Renal * Creatinine no greater than 2.0 mg/dL Cardiovascular * No myocardial infarction within the past 6 months * No uncontrolled high blood pressure * No unstable angina * No serious uncontrolled cardiac arrhythmia * No active congestive heart failure Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 30 days after study participation * HIV negative * No other malignancy within the past 5 years except carcinoma in situ of the cervix, resected basal cell or squamous cell skin cancer, or prostate cancer that is in remission after a radical retropubic prostatectomy or radiotherapy * No medical or psychiatric condition that makes the patient a poor risk for this study * No active or uncontrolled infection * No known hypersensitivity to rituximab or its components or to murine proteins PRIOR CONCURRENT THERAPY: Biologic therapy * No prior biologic therapy for mantle cell lymphoma Chemotherapy * No prior chemotherapy for mantle cell lymphoma Endocrine therapy * No prior endocrine therapy for mantle cell lymphoma Radiotherapy * No prior radiotherapy Surgery * Prior splenectomy allowed (for diagnosis, cytopenia, or symptomatic splenomegaly)