A Phase II/III Randomized Study of R-MiniCHOP With or Without CC-486 (Oral Azacitidine) in Participants Age 75 Years or Older With Newly Diagnosed Diffuse Large B Cell Lymphoma, Grade IIIB Follicular Lymphoma, Transformed Lymphoma, and High-Grade B-Cell Lymphomas With MYC AND BCL2 and/or BCL6 Rearrangements

• Participants must have histologically or cytologically confirmed diffuse large B-cell lymphoma (DLBCL), Ann Arbor Stage IIX (bulky), III or IV. Participants with DLBCL transformed from follicular lymphoma (FL) or marginal zone lymphoma (MZL, including mucosa-associated lymphoid tissue [MALT] lymphomas), lymphoplasmacytic lymphoma (LPL), or nodular lymphocyte-predominant Hodgkin Lymphoma (NLPHL) are eligible. Participants with Grade IIIB follicular lymphoma (FL) or high-grade B-cell lymphomas with MYC and BCL2 and/or BCL6 rearrangements are also eligible. Participants with DLBCL that arose from prior CLL (Richter's transformation) are not eligible.

• As defined by the World Health Organization (WHO), eligible lymphoma subtypes include the following:

• DLBCL, not otherwise specified (NOS)

• DLBCL, germinal-center B-cell type (GCB)

• DLBCL, activated B-cell type (ABC)

• T-cell histiocyte-rich B-cell lymphomas (THRBCL)

• Primary cutaneous DLBCL, leg type

• Intravascular large B cell lymphoma

• EBV+ DLBCL, NOS

• DLBCL associated with chronic inflammation

• HHV8+ DLBCL, NOS

• High-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 rearrangements

• High grade B-cell lymphoma, NOS

• Follicular lymphoma grade 3b

• Participants must have staging imaging performed within 28 days prior to registration, as follows. Positron emission tomography (PET)-computed tomography (CT) baseline scans are strongly preferred; diagnostic quality magnetic resonance imaging (MRI), contrast-enhanced CT, or contrast-enhanced MRI scans are also acceptable if PET-CT is not feasible at baseline. Note: PET-CT will be required at end of treatment (EOT) and progression for response assessment. All measurable lesions (longest diameter >= 1.5 cm) must be assessed within 28 days prior to registration. Tests to assess non-measurable disease must be performed within 42 days prior to registration.

• Participants with known human immunodeficiency virus (HIV)-infection are eligible providing they are on effective anti-retroviral therapy and have undetectable viral load at their most recent viral load test (must be within 26 weeks prior to registration). Participants with known HIV must have a CD4 count checked within 28 days prior to registration, but may proceed with therapy regardless of CD4 count.

• All participants must be screened for chronic hepatitis B virus (HBV) within 28 days prior to registration. Participants with known HBV infection (positive serology) must also have a HBV viral load performed within 28 days prior to registration, and participants must have an undetectable HBV viral load on suppressive therapy within 28 days prior to registration. Participants found to be HBV carriers during screening are eligible and must receive standard of care prophylaxis. Participants with active hepatitis B (HBV viral load > 500 IU/mL) within 28 days prior to registration are not eligible

• Participants with a known history of hepatitis C virus (HCV) infection must have an undetectable HCV viral load within in 28 days prior to registration

• Participants must have a Zubrod performance status of 0-2

• Participants must have adequate renal function, as demonstrated by a creatinine clearance, calculated by the Cockcroft and Gault formula, of >= 30 ml/min that was obtained within 28 days prior to registration

• Aspartate aminotransferase (AST) =< 2.5 x institutional upper limit of normal (IULN), alanine aminotransferase (ALT) =< 2.5 x IULN (within 28 days prior to registration)

• Total bilirubin =< 2 x institutional upper limit of normal (IULN), unless due to Gilbert's disease, hemolysis, or lymphomatous involvement of liver (within 28 days prior to registration). Note: If total bilirubin is elevated, and direct bilirubin is subsequently performed (within 28 days prior to registration) and resulted to be =< 2 x IULN, the participant will be considered eligible

• Absolute neutrophil count (ANC) >= 1000/mcL (within 28 days prior to registration)

• Platelets >= 75,000/mcL (within 28 days prior to registration)

• Hemoglobin (Hgb) >= 8 g/ dL (within 28 days prior to registration)

• If there is a documented lymphomatous involvement of the bone marrow, bone marrow function within 28 days prior to registration, as evidenced by:

• ANC >= 500/mcL

• Platelets >= 50,000/mcL

• Hemoglobin (Hgb) >= 8 g/ dL

• Participants must have a left ventricular ejection (LVEF) fraction >= 45% as measured by echocardiogram or radionuclide (multigated acquisition scan [MUGA]) ventriculography within 56 days prior to registration

• For the duration of the study treatment period and for at least 4 months following the last dose of study drug, male participants must agree to use effective contraceptive methods during sexual contact with a female of childbearing potential (FCBP) and must agree to refrain from semen or sperm donation during the same timeframe. Effective contraceptive methods include a history of vasectomy, use of hormonal contraception or an intrauterine device (IUD) by the female partner, or use of condoms

• A FCBP is a sexually mature woman who: 1) has not undergone a hysterectomy or bilateral oophorectomy; or 2) has not been naturally postmenopausal for at least 24 consecutive months (i.e., has had menses at any time in the preceding 24 consecutive months)