Efficacy and Safety of Treatment With a Single Dose of 90Y-ibritumomab Tiuxetan in Patients With Low Tumor Burden Untreated or Indolent NHL

Inclusion Criteria: * histologically confirmed indolent lymphoma including: * follicular grade 1 or 2 * small lymphocytic * marginal zone (nodal) * marginal zone (splenic) * mucosa associated lymphoid tissue (MALT) * no evidence of transformation * Stage III or IV disease * No prior therapy * involvement by less than 25% of bone marrow on assessment of trephine biopsy * absolute lymphocyte count ≤ x 109/L * platelets ≥ 150 x 109/L * hemoglobin ≥ 100g/L * absolute neutrophil count ≥ 1.5 x 109/L * at least one bidimensionally measurable lesion at least 2cm by CT scanning Exclusion Criteria: * any other anticancer treatment for NHL * prior radiation therapy * prior myeloablative therapy (bone marrow or peripheral blood stem cell transplant) * no other malignancy within the past 10 years except adequately treated non-melanoma skin tumors or carcinoma in situ of the cervix * presence of central nervous system lymphoma * patients known to be HIV positive * patients with known seropositivity for Hepatitis C virus, Hepatitis B virus or other active infection uncontrolled by treatment * patients with abnormal liver function: total bilirubin \> 1.5X ULN or ALT \> 2.5X ULN * patients with abnormal renal function: serum creatinine \> 2.5X ULN * known hypersensitivity to murine antibodies or proteins * immunotherapy during the preceding 6 months (including monoclonal antibodies, interleukins, interferon)