RATIONALE: Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die. Monoclonal antibodies such as rituximab can locate cancer cells and either kill them or deliver cancer-killing substances to them without harming normal cells. Combining chemotherapy with monoclonal antibody therapy may kill more cancer cells.

PURPOSE: Phase II trial to study the effectiveness of combining pentostatin and rituximab in treating patients who have non-Hodgkin's lymphoma or chronic lymphocytic leukemia.

OBJECTIVES:

• Determine the response rate in patients with low-grade B-cell non-Hodgkin's lymphoma or chronic lymphocytic leukemia treated with pentostatin and rituximab.
• Determine the duration of response, median time to progression, and survival of patients treated with this regimen.
• Determine the safety of this regimen in these patients.

OUTLINE: This is a multicenter study.

Patients receive rituximab IV alone on day 1 of course 1 only. Patients then receive rituximab IV and pentostatin IV on days 8, 15, and 22. An additional course with both drugs is administered on days 36, 43, and 50. Patients with progressive disease or a complete response receive no further treatment. Patients with responsive disease, but less than a complete response, receive one additional course of therapy as above.

Patients are followed every 3 months.

PROJECTED ACCRUAL: A total of 50 non-Hodgkin's lymphoma and 50 chronic lymphocytic leukemia patients will be accrued for this study.

• Leukemia
• Lymphoma

• Biological: rituximab
• Drug: pentostatin

DISEASE CHARACTERISTICS:

• Histologically confirmed low-grade non-Hodgkin's lymphoma

  • REAL classification:

    • B-cell chronic lymphocytic leukemia
    • Prolymphocytic leukemia
    • Small lymphocytic lymphoma
    • Follicular center lymphoma (grade I, II, or III)
    • Extranodal marginal zone B-cell lymphoma Malt type

  • International Working Group classification:

    • Small lymphocytic/chronic lymphocytic leukemia (CLL)

      • CLL with lymph node involvement allowed
    • Small lymphocytic plasmacytoid
    • Follicular small cleaved cell
    • Follicular mixed small and large cell
    • Follicular predominantly large cell

• Measurable disease

  • Lymph node more than 1 cm in longest transverse diameter NOTE: 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:

• ECOG 0-2

Life expectancy:

• More than 6 months

Hematopoietic:

• Absolute neutrophil count at least 1,000/mm^3
• Platelet count at least 75,000/mm^3
• Hemoglobin at least 9 g/dL

Hepatic:

• Bilirubin no greater than 2.0 mg/dL
• AST no greater than 5 times upper limit of normal

Renal:

• Creatinine less than 2.0 mg/dL
• BUN normal
• Urinalysis normal

Cardiovascular:

• LVEF normal in patients with history of stable heart disease for at least 2 years

Other:

• HIV negative
• No thyroid disease with thyroid function that cannot be maintained in the normal range
• No other prior malignancy unless progression free for more than 5 years
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Prior rituximab, Y2B8, or iodine I 131 tositumomab allowed provided at least 6 months have elapsed and patient has had clear disease progression
• No other concurrent immunotherapy

Chemotherapy:

• No more than 6 prior chemotherapy drugs
• No more than 3 prior treatments with pentostatin
• At least 3 weeks since prior chemotherapy
• No prior cumulative lifetime dose of more than 480 mg/m2 of doxorubicin or an equivalent dose of any anthracycline
• No other concurrent chemotherapy

Endocrine therapy:

• Not specified

Radiotherapy:

• No concurrent radiotherapy to an indicator lesion

Surgery:

• Not specified

Other:

• No other concurrent investigational drug