Rituximab Plus Lenalidomide for Patients With Relapsed / Refractory Indolent Non-Hodgkin's Lymphoma (Follicular Lymphoma and Marginal Zone Lymphoma)

Inclusion Criteria:

* Age ≥18 years at the time of signing the informed consent document.
* Understand and voluntarily sign an informed consent document prior to any study related assessments/procedures are conducted.
* Histologically confirmed marginal zone lymphoma or follicular lymphoma (grade 1, 2 or 3a; CD20+ by flow cytometry or histochemistry).
* Previously treated with at least one prior systemic chemotherapy, immunotherapy or chemoimmunotherapy and have received at least 2 previous doses of rituximab.
* Documented relapsed, refractory or progressive disease after treatment with systemic therapy and must not be rituximab-refractory.
* Investigator considers rituximab monotherapy appropriate.
* Bi-dimensionally measurable disease on cross sectional imaging by X-ray computed tomography (CT) or magnetic resonance imaging (MRI).
* Need of treatment for relapsed, progressed or refractory disease as assessed by the investigator.
* Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2.
* Adequate bone marrow function.
* Willingness to follow study visit schedule, pregnancy precautions and other protocol requirements.

Exclusion Criteria:

* Histology other than follicular or marginal zone lymphoma or clinical evidence of transformation or Grade 3b follicular lymphoma.
* Subjects taking corticosteroids during the last week prior to study treatment, unless administered at a dose equivalent to \< 20 mg/day prednisone or prednisolone.
* Systemic anti-lymphoma therapy within 28 days or use of antibody agents within 8 weeks use of radioimmunotherapy within 6 months.
* Known seropositive for or active viral infection with hepatitis B virus (HBV) or/and human immunodeficiency virus (HIV).
* Known hepatitis C virus (HCV) positive with chronic HCV or active viral infection with HCV hepatitis requiring anti-viral medication (at time of randomization).
* Life expectancy \< 6 months.
* Known sensitivity or allergy to murine products.
* Prior history of malignancies, other than follicular or marginal zone lymphoma, unless the subject has been free of the disease for ≥ 5 years.
* Prior use of lenalidomide.
* Known allergy to thalidomide.
* Neuropathy \> Grade 1.
* Presence or history of central nervous system involvement by lymphoma.
* Subjects who are at a risk for a thromboembolic event and are not willing to take prophylaxis for it.
* Uncontrolled intercurrent illness.
* Any significant medical condition, laboratory abnormality, or psychiatric illness that would prevent the subject from signing the informed consent document.
* Pregnant or lactating females.
* Any condition that places the subject at unacceptable risk if he/she were to participate in the study or that confounds the ability to interpret data from the study.