A Study of Epcoritamab With Lenalidomide and Tafasitamab in People With Diffuse Large B Cell Lymphoma

Inclusion Criteria: * Age ≥ 18 years * Pathologically confirmed diffuse large B cell lymphoma, transformed indolent lymphoma, primary mediastinal B cell lymphoma, high grade B cell lymphoma, follicular lymphoma grade 3B * Subjects must have histologically confirmed CD20+ lymphoma as documented in the most recent representative pathology report. * Presence of CD19 is not required to be confirmed (except if patients have received anti-CD19 therapy in the past). Patients treated with prior anti-CD19 therapy must have confirmation of CD19 expression in a biopsy done after progression on the last CD19 directed therapy. * At least 2 prior lines of systemic therapy including CART or ASCT (up to 4 prior lines of therapy allowed). Note that bridging therapy prior to ASCT or CART will be counted as a separate line of therapy) * At least one prior line of systemic therapy for patients ineligible for ASCT/CART or patients unwilling to undergo CAR-T/ASCT for logistic or other reasons (up to 4 prior lines of therapy allowed) * Have radiologically measurable lymphadenopathy or extranodal involvement. * Eastern Cooperative Oncology Group performance status (PS) ≤ 2 (ECOG \>2 can be enrolled if PS compromised from lymphoma e.g. spinal cord compression and expected to improve rapidly with therapy) * Must have adequate organ and marrow status Hemoglobin ≥8 g/dL (red blood cell transfusions are allowed) * Absolute neutrophil count (ANC) ≥1,000/mm\^3 or ≥500/mm\^3 if due to disease involvemen…