A Phase III, Open-Label, Prospective, Two-Armed, Multicenter, Randomized, Group Sequential Study to Evaluate the Efficacy and Safety of Subsequent Treatment With the Zevalin (Ibritumomab Tiuxetan) Study Regimen Versus Observation in Patients With Diffuse Large B-Cell Lymphoma Who Are in Complete Remission After First-Line CHOP-Rituximab (CHOP-R) Therapy

Inclusion Criteria:

- Histologically confirmed, Ann Arbor stage II, III, or IV DLBCL according to the
REAL/WHO classification (from initial diagnosis made prior to starting CHOP-R
therapy)

- Central pathology review confirming the DLBCL diagnosis and CD20 positivity, and no
evidence of DLBCL in bone marrow

- First-line treatment of DLBCL must have been 6 or 8 cycles of standard CHOP
chemotherapy (cyclophosphamide 750 mg/m2, doxorubicin 50 mg/m2, vincristine 1.4 mg/m2
up to a maximum of 2 mg on day 1, and at least 40 mg/m2/day prednisone on Days 1 to 5
every three weeks, with generally accepted adjustments in dose or frequency due to
toxicity, patient scheduling, etc.) in combination with rituximab (375 mg/m2)

- Complete remission (CR) or unconfirmed complete remission (CRu) according to the
International Workshop Response Criteria for NHL described by Cheson et al and
modified for this study after first-line treatment with CHOP-R. CT scans of chest,
abdomen, pelvis, and neck (if applicable) must have been performed within 6 weeks
after the last dose of the last course of CHOP-R. Applicability of the neck CT means
that the patient had involvement of the neck region by palpation / physical
examination at first diagnosis (pre-CHOP-R).

- Central radiographic review of the CT scans (chest, abdomen, pelvis and if
applicable, neck) from before and after first-line treatment with CHOP-R fulfilling
the radiological requirements for CR/CRu

- Patients 60 years of age or older at time of randomization

- WHO performance status (PS) of 0 to 2 within 1 week of randomization

- Absolute neutrophil count (ANC)greater than or equal to 1.5 x 10^9/L within 1 week of
randomization

- Hemoglobin (Hgb) greater than or equal to 10 g/dL within 1 week of randomization

- Platelets greater than or equal to 150 x 10^9/L within 1 week of randomization

- Life expectancy of 3 months or longer

- Written informed consent obtained according to local guidelines

Exclusion Criteria:

- Presence of any other malignancy or history of prior malignancy except non-melanoma
skin tumors or stage 0 (in situ) cervical carcinoma

- Prior radioimmunotherapy, radiation therapy, or any other NHL therapy except
first-line CHOP-R

- Presence of gastric, central nervous system (CNS), or testicular lymphoma at first
diagnosis

- Histological transformation of low-grade NHL

- Known seropositivity for hepatitis C virus (HCV) or hepatitis B surface antigen
(HbsAg)

- Known history of HIV infection

- Abnormal liver function: total bilirubin > 1.5 x ULN or ALT > 2.5 x ULN within 1 week
of randomization

- Abnormal renal function: serum creatinine > 2.0 x ULN within 1 week of randomization

- Nonrecovery from the toxic effects of CHOP-R therapy

- Known hypersensitivity to murine or chimeric antibodies or proteins

- G-CSF or GM-CSF therapy within two weeks (or four weeks if pegylated) prior to
screening laboratory sampling

- Concurrent severe and/or uncontrolled medical disease (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

- Male and female patients of child-bearing potential unwilling to practice effective
contraception during the study and unwilling or unable to continue contraception for
12 months after their last dose of study treatment

- Female patients who are pregnant or are currently breastfeeding

- Treatment with investigational drugs less than 4 weeks before the planned Day 1 or
nonrecovery from the toxic effects of such therapy

- Surgery less than 4 weeks before the planned Day 1 or nonrecovery from the side
effects of such surgery

- Concurrent systemic corticosteroid use for any reason except as premedication in case
of known or suspected allergies to contrast media or as premedication for potential
side effects of rituximab treatment

- Unwillingness or inability to comply with the protocol