Diffuse large B cell lymphoma (DLBCL) is an aggressive but potentially curable malignancy; however, cure is highly dependent on the ability to deliver intensive, anthracycline-based chemoimmunotherapy. Nearly one third of cases of DLBCL occur in patients over age 75 years, and advanced age is an important adverse feature in prognostic models. Despite this incidence in older patients, there is no clear accepted standard of care due to under-representation of this group in large randomized clinical trials. Furthermore, insufficient assessments of baseline frailty and prediction of toxicity hamper clinical decision-making. Here, we present an ongoing randomized study of R-miniCHOP chemoimmunotherapy with or without oral azacitidine (CC-486, Onureg) for patients age 75 and older with newly diagnosed DLBCL and associated aggressive lymphomas. The incorporation of an oral hypomethylating agent is based on increased tumor methylation as a biologic feature of older patients with DLBCL and a desire to minimize the injection burden for this population. This is the first randomized study in this population conducted in North America by the National Clinical Trials Network (NCTN) and will enroll up to 422 patients including 40 patients in a safety run-in phase. This study incorporates an objective assessment of baseline frailty (the FIL Tool) and a serial comprehensive geriatric assessment (CGA). Key correlative tests will include circulating tumor DNA (ctDNA) assays at pre-specified timepoints to explore if ctDNA quantity and methylation patterns correlate with response. S1918 has the potential to impact future trial design and to change the standard of care for patients 75 years and older with aggressive lymphoma given its randomized design, prospective incorporation of geriatric assessments, and exploration of ctDNA correlatives. Trial registration: The trial is registered with ClinicalTrial.gov Identifier NCT04799275.