Phase II Trial With Correlative Laboratory Studies of Single Agent Irinotecan (Camptosar CPT-11)

DISEASE CHARACTERISTICS: Histologically proven newly diagnosed or relapsed non-Hodgkin's lymphoma (NHL) of 1 of the following types: Low grade (diffuse small lymphocytic/marginal zone, grade I follicular small cleaved cell, or grade II follicular mixed cell) OR Mantle cell OR Histologically proven newly diagnosed or relapsed stage III or IV chronic lymphocytic leukemia (CLL) or prolymphocytic leukemia (PLL) At least 1 measurable disease parameter Enlarged spleen extending at least 2 cm below the costal margin constitutes measurable disease provided that no explanation other than lymphomatous involvement is likely Enlarged liver extending at least 5 cm below the costal margin constitutes measurable disease Not allowable as sole indication for therapy: Isolated splenomegaly OR Isolated hepatomegaly No central nervous system (CNS) metastases or carcinomatous meningitis A new classification scheme for adult non-Hodgkin's lymphoma has been adopted by PDQ. The terminology of "indolent" or "aggressive" lymphoma will replace the former terminology of "low", "intermediate", or "high" grade lymphoma. However, this protocol uses the former terminology. PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Eastern Cooperative Oncology Group (ECOG) 0-2 Life expectancy: At least 12 weeks Hematopoietic: NHL: Granulocyte count greater than 1,500/mm\^3 Hemoglobin at least 9.0 g/dL Platelet count greater than 100,000/mm\^3 CLL or PLL: Granulocyte count greater than 500/mm\^3 Hemoglobin greater than 7.0 g/dL Platelet count greater than 50,000/mm\^3 Hepatic: Bilirubin no greater than 1.5 mg/dL SGOT no greater than 3 times upper limit of normal (ULN) (no greater than 5 times ULN if liver tumor present) No Gilbert's disease Renal: Creatinine no greater than 2.0 mg/dL OR Creatinine clearance at least 60 mL/min Calcium less than 12.0 mg/dL (corrected) Cardiovascular: No myocardial infarction or atrial fibrillation within the past 6 months No congestive heart failure requiring therapy Other: No active or uncontrolled infection HIV negative No psychiatric disorder that would preclude informed consent or compliance No other malignancy within the past 5 years except basal cell or squamous cell skin cancer or carcinoma in situ of the cervix Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No history of seizures No uncontrolled diabetes mellitus, defined as random blood glucose at least 200 mg/dL No other severe concurrent disease that would increase risk PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior irinotecan or any other topoisomerase I inhibitor (e.g., topotecan) Endocrine therapy: Not specified Radiotherapy: Not specified Surgery: Not specified Other: No concurrent phenytoin, phenobarbital, or other antiepileptic prophylaxis