Efficacy and safety of a single dose of 14.8 MBq/kg (0.4 mCi/kg)90Y-ibritumomab tiuxetan ("Zevalin") in elderly patients with diffuse large B-cell lymphoma and FDG-PET positive partial remission following first-line R-CHOP therapy. A Phase II clinical trial (HOVON 77).

1. Age >= 60 years old;

2. WHO performance status of 0-2;

3. Life expectancy of at least 3 months;

4. Histologically confirmed CD20 positive Diffuse large B-cell lymphoma (DLBCL), according to the WHO classification;

5. First-line induction treatment with R-CHOP or R-CHOP-like chemotherapy (only CHOP in combination with rituximab; CHOP14 and CHOP21 are both allowed);

6. Partial response on CT-scans after first-line treatment, with measurable disease;

7. PET-positive residual mass;

8. Patient is not eligible for high dose chemotherapy followed by autologous stem cell transplantation;

9. Less than 25% bone marrow involvement at the end of first-line treatment during PR analysis (measurement in a representative bone marrow biopsy);

10. Absolute neutrophil count (ANC) >= 1.5x10^9/l;

11. Hemoglobin (Hb) >= 6 mmol/l;

12. Platelets >= 150 x 10^9/l;

13. Written informed consent obtained according to local guidelines.

1. Hypoplastic bone marrow at biopsy;

2. Prolonged pancytopenia during induction chemotherapy and delayed courses during R-CHOP induction (more than two weeks delay due to insufficient bone marrow reserve);

3. Known hypersensitivity to murine antibodies or proteins;

4. Significant splenomegaly;

5. Patients with abnormal liver function (total bilirubin > 2.0 x ULN);

6. Patients with abnormal renal function (serum creatinine > 2.0 x ULN);

7. Presence of CNS involvement by NHL;

8. Presence of any other active neoplasms or history of prior malignancy, except non-melanoma skin tumours or stage 0 (in situ) cervical carcinoma during the past 5 years;

9. More than one prior R-CHOP or R-CHOP-like chemotherapy regimen for DLBCL;

10. Patients who have received prior external beam radiotherapy to > 25% of active bone marrow (involved field or regional);

11. Patients who have received G-CSF or GM-CSF therapy within two weeks prior to study enrollment;

12. Concurrent severe and/or uncontrolled medical condition (e.g. uncontrolled diabetes, congestive heart failure, myocardial infarction within 6 months of study, unstable and uncontrolled hypertension, chronic renal disease, or active uncontrolled infection) which could compromise participation in the study;

13. Patients who have received biologic therapy, immunotherapy, R-CHOP(-like) chemotherapy, surgery, or an investigational drugs less than 4 weeks prior to first day of study treatment or who have not recovered from the toxic effects of such therapy;

14. Patients who have received systemic corticosteroids at doses higher than 20 mg/day prednisolone or equivalent less than 2 weeks prior to 90Y-ibritumomab tiuxetan administration;

15. Known diagnosis of HIV infection;

16. Patients unwilling or unable to comply with the protocol.