Inclusion Criteria:

          -  Phase I: Histological confirmation of expressing CD20 antigen as determined by
             pathology at the respective institution and central pathology review at Mayo Clinic
             Rochester; all types of B-cell lymphomas are allowed to participate; patients with
             primary mediastinal large B-cell (PMLBCL) or transformed lymphoma are allowed to
             participate

          -  Phase II: Histological confirmation of DLBCL expressing CD20 antigen as determined by
             pathology at the respective institution and central pathology review at Mayo Clinic
             Rochester; patients with primary mediastinal large B-cell (PMLBCL) or transformed
             lymphoma are not allowed to participate

          -  Measurable disease (at least 1 lesion >= 1.5 cm in diameter) as detected by PET/CT

          -  Only 1 line of previous anti-lymphoma therapy is allowed and not currently receiving
             any other agent that would be considered as a treatment for the lymphoma; patients
             must be >= 2 weeks from prior anti-lymphoma therapy; the use of steroids and/or
             rituximab up to 1 week prior to registration for management of symptoms is allowed

          -  Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-2

          -  Absolute neutrophil count (ANC) >= 1500/mm^3, obtained =< 7 days prior to registration

          -  Platelet count >= 75,000/mm^3, obtained =< 7 days prior to registration

          -  Total bilirubin =< 2 x upper limit of normal (ULN) (unless related to lymphoma or
             Gilbert's disease) OR =< 5 x ULN for subjects with documented or suspected Gilbert's
             disease, or related to involvement of the liver by the lymphoma, obtained =< 7 days
             prior to registration

          -  Aspartate transaminase (AST) and alanine aminotransferase (ALT) (serum glutamate
             pyruvate transaminase [SGPT]) =< 3 x ULN unless evidence of the direct liver and/or
             bone involvement by lymphoma, then =< 5 x ULN, obtained =< 7 days prior to
             registration

          -  PHASE I: Subjects must have calculated creatinine clearance >= 60 ml/min by
             Cockcroft-Gault formula, obtained =< 7 days prior to registration

          -  PHASE II: Subjects must have calculated creatinine clearance >= 30 ml/min by
             Cockcroft-Gault formula, obtained =< 7 days prior to registration

          -  For women of childbearing potential only: Negative pregnancy test =< 10-14 days prior
             to registration; NOTE: the patient must have an additional negative pregnancy test =<
             24 hours prior to receiving the initial prescription of lenalidomide, per requirements
             of the REVLIMID Risk Evaluation and Mitigation Strategies (REMS) program

          -  Provide informed written consent

          -  Willing to return to enrolling institution for follow-up (during the active monitoring
             phase of the study [i.e. active treatment and observation])

          -  Willing to provide blood samples for correlative research purposes

          -  Considered transplant-eligible, as determined by the opinion of the investigator at
             the participating institution; the participating institution does not need to be a
             transplant center but patients can be referred to a transplant center if needed

          -  Willing and able to register into and comply with the mandatory requirements of
             Celgene's REVLIMID REMS program

          -  Females of reproductive potential are willing and able to adhere to the scheduled
             pregnancy testing as required by Celgene's REVLIMID REMS program

          -  Willing and able to take aspirin (81 mg) daily as prophylactic anticoagulation
             (patients intolerant to acetylsalicylic acid [ASA] may use warfarin or low molecular
             weight heparin)

        Exclusion Criteria:

          -  Any of the following because this study involves an agent that has known genotoxic,
             mutagenic and teratogenic effects:

               -  Pregnant women

               -  Nursing women

               -  Men or women of childbearing potential who are unwilling to employ adequate
                  contraception

                    -  NOTE: patients unwilling or unable to do any of the following are also
                       excluded:

                         -  Men must agree to use a latex condom during sexual contact with a
                            female of child-bearing potential even if they have had a successful
                            vasectomy

                         -  Women of child bearing potential must agree to use 2 methods of
                            reliable contraception simultaneously

                         -  All patients must be counseled at a minimum of every 28 days about
                            pregnancy precautions and risks of fetal exposure

          -  Co-morbid systemic illnesses or other severe concurrent disease which, in the judgment
             of the investigator, would make the patient inappropriate for entry into this study or
             interfere significantly with the proper assessment of safety and toxicity of the
             prescribed regimens including, but not limited to, ongoing or active infection,
             symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or
             psychiatric illness/social situations that would limit compliance with study
             requirements

          -  Immunocompromised patients and patients known to be human immunodeficiency virus (HIV)
             positive and currently receiving antiretroviral therapy; NOTE: patients known to be
             HIV positive, but without clinical evidence of an immunocompromised state, are
             eligible for this trial; patients with HIV on antiretroviral therapy other than
             zidovudine (AZT) and/or stavudine and without prior acquired immunodeficiency syndrome
             (AIDS) defining conditions and adequate CD4 count (> 400) are eligible

          -  History of myocardial infarction =< 180 days prior to registration or congestive heart
             failure requiring use of ongoing maintenance therapy for life-threatening ventricular
             arrhythmias

          -  Receiving any other investigational agent which would be considered as a treatment for
             the primary neoplasm; patients must be >= 2 weeks from prior anti-lymphoma therapy;
             the use of steroids and/or rituximab up to 1 week prior to registration for management
             of symptoms is allowed

          -  Other active malignancy =< 3 years prior to registration; EXCEPTIONS: non-melanotic
             skin cancer, carcinoma-in-situ of the cervix, or any cancer that, in the judgment of
             the investigator, has been treated with curative intent and will not interfere with
             the study treatment plan and response assessment; NOTE: if there is a history of prior
             malignancy, they must not be receiving other specific treatment such as radiation,
             chemotherapy, or immunotherapy for their cancer

          -  Unable or unwilling to take any prophylaxis; patients with history of or new/active
             deep vein thrombosis/embolism/thrombophilia are allowed to participate if they are on
             appropriate therapeutic anticoagulation during the treatment on the trial; these
             patients would not need the aspirin with the lenalidomide unless clinically indicated;
             therefore, patients must be able and willing to receive anticoagulation (prophylaxis
             versus therapeutic as clinically indicated)

          -  History of radiation therapy to >= 25% of the bone marrow for other diseases

          -  Receiving erythroid stimulating agents (epoetin alfa [EPO]: Procrit, Aranesp)

          -  Patients with active or prior central nervous system (CNS) lymphoma or cerebrospinal
             fluid involvement with malignant lymphoma cells; NOTE: these patients are usually
             treated with CNS directed therapy; screening for cerebrospinal fluid (CSF)/CNS
             involvement is NOT required but can be performed per treating medical doctor (MD)
             discretion

          -  Active hepatitis B as defined by seropositivity for hepatitis B surface antigen
             (HBsAg); subjects with positive hepatitis B core antibody titers and normal liver
             transaminases are allowed provided that antiviral prophylaxis is administered per
             institutional guidelines; NOTE: subjects with hepatitis C antibody will be eligible
             provided that they do not have elevated liver transaminases or other evidence of
             active hepatitis