Background: SDZ-RTX (Rixathon) is approved in more than 20 countries and regions, including highly regulated markets e.g. Europe, Japan and Switzerland for all labeled indications of reference rituximab. REFLECT is the first prospective post-approval study to evaluate a rituximab biosimilar as a curative therapy in untreated pts with CD20⁺ DLBCL. This interim analysis adds up efficacy and additional safety results on the previously presented data (Welslau et al, ASCO and EHA 2019). Methods: Adult patients (pts) were treated with SDZ-RTX and cyclophosphamide, doxorubicin, vincristine, prednisone (R-CHOP) according to the product label. The primary endpoint is to evaluate the effectiveness of Rixathon measured by complete response (CR) rate at the end of treatment. Secondary endpoints are overall response rate (ORR), progression-free survival at 24 months and adverse events (AEs). Data were collected at baseline and all scheduled treatment and follow-up visits, which is still ongoing. No imputation was made for missing values, and endpoints are summarized descriptively. Results: As of Sep 30, 2019, 170 pts were enrolled, and R-CHOP treatment was close to completion. The median age of pts was 70 years, and 52% were women. Overall, 38% of pts completed the first 12-month observation period, 41% were ongoing, while 21% of pts discontinued. Most of the pts (~80%) had an ECOG score of 0 (35%) or 1 (46%). Early staging (I–II2), low to intermediate disease risk (IPI 0-2), and known B symptoms were reported for 55%, 50%, and 30% of pts, respectively. CR rate at the end of treatment was 57% (defined as the revised response criteria for malignant lymphoma by Cheson et al, 2007 that excludes complete remission/unconfirmed [CRu]). Summary of efficacy is reported in the Table. Overall, 83% of pts experienced AEs, the most common being anemia (23%), fatigue (21%), and polyneuropathy (15%). Treatment-related AEs were reported for 28% of pts. Rates of any serious AEs (SAEs) and treatment-related SAEs were 37% and 6.5%, respectively. On-treatment deaths and all deaths were reported in 2.4% and 4.7% of pts, respectively. Conclusions: REFLECT is the first prospective post-approval study to evaluate a rituximab biosimilar as a curative therapy in untreated pts with DLBCL. This interim analysis results re-confirms the expected safety and efficacy profile for DLBCL patients treated with R-CHOP.