Background The combination of the anti-CD19 monoclonal antibody tafasitamab and the immune modulatory drug lenalidomide (LEN) has been commercially available in the US for adult patients with relapsed/refractory diffuse large B-cell lymphoma (R/R DLBCL) not otherwise specified, including DLBCL arising from low-grade lymphoma, and who are ineligible for autologous stem cell transplant (ASCT) since August 05, 2020. It was granted accelerated FDA approval and EU conditional marketing authorization after the primary analysis of Phase II L-MIND study (NCT02399085) demonstrated safety and efficacy in this setting. To complement clinical data, it is important to assess real-world safety and effectiveness given the heterogeneity of routine clinical care. Furthermore, focusing on patients from racial and ethnic minorities, who may face challenges in receiving optimal access to care, may help to identify and address inequities. realMIND is an observational study of the real-world safety and effectiveness of tafasitamab + LEN for the treatment of R/R DLBCL among patients in the US by race and ethnicity. Using prospective and, where necessary, retrospective data collection, this non-interventional study will also provide a deeper understanding of treatment patterns of US patients with R/R DLBCL treated with tafasitamab, and its use in a real-world setting in terms of treatment duration, dose modifications, and post-tafasitamab + LEN combination partners and monotherapy use. Methods realMIND (NCT04981795) is a multicenter, observational, prospective and retrospective Phase IV trial-in-progress study targeting ≥100 US patients with R/R DLBCL treated with tafasitamab + LEN. To ensure diversity, Group 1 will enroll patients from racial and ethnic minorities (n≥50), while Group 2 will comprise non-Hispanic White (NHW) patients (n≥50) (Figure 1). Eligible patients are ≥18 years old with histologically confirmed R/R DLBCL, ≥1 prior line of treatment, and have initiated or will be initiating tafasitamab treatment (except in the context of an interventional study). Prospective data collection began at study sites in September 2021, and retrospective data (from study sites or vendor databases) may include patients with a tafasitamab start date (index date) from August 05, 2020, onwards. The primary endpoints include safety and effectiveness outcomes (Table 1). Serious adverse events (SAEs) and treatment-emergent adverse events (TEAEs) will be reported. Effectiveness will be assessed in terms of tumor response rates and time-to-event endpoints, while secondary endpoints include treatment line and dose information (Table 1). Patient data for this observational study will be collected by prospective follow-up of patients included at study sites, or by retrospective collection of data from patient records, at study sites or from vendor databases. Prospective and retrospective data will be analyzed separately, as well as pooled. No formal sample size calculation was performed due to the descriptive nature of the study and no hypothesis testing is planned. Study status The in-progress non-interventional realMIND study is expected to end by approximately December 2025, or earlier, when: ≥50 patients treated with tafasitamab + LEN have been recruited into each of Group 1 and Group 2 with either prospective or retrospective data collection; and all prospectively-followed patients have ≥6 months follow-up after starting tafasitamab treatment, or have discontinued from the study for any reason, whichever occurs earlier. The results are anticipated to describe the real-world safety and effectiveness of tafasitamab for R/R DLBCL in US patients, with a focus on underrepresented racial and ethnic minorities, to help optimize outcomes of treatment and identify opportunities for further studies.