Percentage of participants having best response of Complete Response (CR) or Partial Response (PR) as per Independent Review Committee and investigator's assessment.

Progression-Free Survival as assessed by the investigator using the Lugano Response Criteria for Malignant Lymphoma

PD, positron emission tomography (PET): score 4 (uptake moderately \> liver) or 5 (uptake markedly higher than liver and/or new lesions) for lymph node/extra lymphatic sites with increase in intensity of Baseline uptake and/or new fluorodeoxyglucose (FDG)-avid foci consistent with lymphoma at interim/end-of-treatment assessment; new/recurrent FDG-avid foci in bone marrow; new FDG-avid foci consistent with lymphoma versus other etiology in new lesions. PD, computed tomography (CT): abnormal individual node/lesion with longest diameter (LDi ) \>1.5 centimeters (cm) and increase by ≥50% from the product of the perpendicular diameters (PPD) nadir and increase in LDi or shortest diameter (SDi) from nadir; new/clear progression of preexisting nontarget lesions; new/recurrent splenomegaly and bone marrow involvement; regrowth of previously resolved lesions. New node \>1.5 cm in any axis. New extranodal site \>1.0 cm in any axis; if \<1.0 cm, presence is unequivocal and attributable to lymphoma.

PD, PET: score 4 (uptake moderately \> liver) or 5 (uptake markedly higher than liver and/or new lesions) for lymph node/extra lymphatic sites with increase in intensity of Baseline uptake and/or new FDG-avid foci consistent with lymphoma at interim/end-of-treatment assessment; new/recurrent FDG-avid foci in bone marrow; new FDG-avid foci consistent with lymphoma versus other etiology in new lesions. PD, CT: abnormal individual node/lesion with LDi \>1.5 cm and increase by ≥50% from the PPD nadir and increase in LDi or SDi from nadir; new/clear progression of preexisting nontarget lesions; new/recurrent splenomegaly and bone marrow involvement; regrowth of previously resolved lesions. New node \>1.5 cm in any axis. New extranodal site \>1.0 cm in any axis; if \<1.0 cm, presence is unequivocal and attributable to lymphoma. Kaplan-Meier estimates indicate the percent probability of a participant being alive at the indicated time after treatment start.

The CRR will be determined by IRC and according to IPCG criteria. This endpoint reflects the proportion of patients who can potentially proceed to different consolidation or maintenance strategies to achieve durable responses.

Efficacy of the addition of tafasitamab (tafa) to dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin with our without rituximab (DA-EPOCH±R) will be assessed using the rate of minimal residual disease (MRD) as measured by multiparameter flow cytometry (MFC) in the University of Washington hematopathology lab. Will consider an absolute increase in the rate of MRD- after one cycle to 50% to be a signal of interest (i.e., increase from 28%).

Defined as any Adverse event either reported for the first time or worsening of a pre-existing event after first dose of study drug up to 90 days after the last dose of study drug.

Progression-free survival was defined as the time from randomization to tumor progression or death from any cause.

Progression-free survival was defined as the time from randomization to tumor progression or death from any cause.

An adverse event (AE) was defined as any untoward medical occurrence in a participant temporally associated with the use of study treatment, whether or not considered related to the study treatment. Therefore, an AE could be any unfavorable or unintended sign (including an abnormal laboratory finding) or symptom temporally associated with the use of study treatment. A TEAE was defined as any AE that started or worsened after the first dose of study treatment until 90 days after the last dose of the study treatment. An AE that was present prior to study drug administration but increased in severity after treatment start was also included as a TEAE.

The toxicity grade of TEAEs was graded using the National Cancer Institute-Common Terminology Criteria for Adverse Events version 5.0 (NCI-CTCAE v5.0) using the following definitions: Grade 1: mild; asymptomatic or mild symptoms; clinical or diagnostic observations only; intervention not indicated. Grade 2: moderate; minimal; local or non-invasive intervention indicated; limiting age-appropriate instrumental activities of daily living (refers to preparing meals, shopping for groceries or clothes, using the telephone, managing money, etc.). Grade 3: severe or medically significant but not immediately life threatening; hospitalization or prolongation of hospitalization indicated; disabling; limiting self-care activities of daily living. Grade 4: life-threatening consequences; urgent intervention indicated. Grade 5: death related to AE.

Toxicities will be classified using the NCI Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. The DLT will be based on the tolerability observed during the first cycle. In order for a patient to be assessed for DLT, they must receive at least 75% of lenalidomide dose (16 of the planned 21 days of lenalidomide administration). The maximum tolerated dose of lenalidomide/Tafasitamab will be the highest dose at which fewer than one-third of patients experience dose limiting toxicity. If multiple toxicities are seen, the presence of dose limiting toxicity should be based on the most severe toxicity experienced.

The MTD is the highest dose at which no more than one instance of a DLT is observed among 6 participants treated.

The RP2D is the dose at which the Phase 2 portion of the study will begin enrolling. RP2D will be determined based on all data including available pharmacokinetics (PK), pharmacodynamic (PD), target engagement, efficacy, safety and tolerability data collected during Phase 1

Response to the combination lenalidomide/Tafasitamab treatment is defined as achieving clinical benefit better at three months restaging. That is overall tumor shrinkage within three months of treatment initiation or stable disease at three months restaging. Response criteria will be graded using the Cytologic Response Criteria, Neurologic Response Criteria, and Radiographic Response Criteria developed by the International Workshop to Standardize Baseline Evaluation and Response Criteria in Primary CNS Lymphoma The response rate is defined as the proportion of study participants meeting the definition of response in Efficacy Analysis Set (EAS). Response rate will be summarized by percentage, along with the corresponding exact 95% confidence intervals (CIs).

Adverse events reported for the first time or worsening of a pre-existing event after first dose of study treatment.

Best Response of complete/complete metabolic response or partial/partial metabolic response