e19020 Background: SDZ-RTX is approved in Europe for the same indications as reference rituximab, based on the totality of evidence for biosimilarity. REFLECT, a real-world study of SDZ-RTX as curative therapy for treatment-naïve CD20+ DLBCL, represents the first biosimilar rituximab post-approval study in DLBCL. Methods: The study includes patients (pts) aged ≥18 years, eligible for rituximab and cyclophosphamide, doxorubicin, vincristine, prednisone (R-CHOP). R-CHOP is administered according to product label. The primary endpoint is complete response rate at the end of treatment. Secondary endpoints include overall response rate, progression-free survival at 12 months, and adverse events (AE). Data are collected at baseline and every study visit for 12 months (efficacy) and ≥30 days after last SDZ-RTX dose (safety). No imputation for missing data is planned; endpoints are summarized descriptively. Results: In an interim analysis (cut off: Sep 6, 2018; recruitment approx. 50% complete), the full analysis set comprised 80 pts: 38 males (47.5%) and 42 females (52.5%), with median (min, max) age 68.5 years (23, 91); 70% of pts were aged ≥60 years. In total, 6 pts have discontinued. Most pts had little or no restriction in daily activities; >80% had ECOG score of 0 (34%) or 1 (50%). B-symptoms were reported in 15 pts (19%). Extranodal infiltration was observed in 40 pts (50%) and bulky disease was observed in 9 pts (11.3%). Most pts had early stage (I–IIB: 63.8%), low to intermediate risk disease (IPI Score 0–2: 61.3%). A summary of safety is reported in the Table. AEs were reported in 53 (66%) pts and 19 (24%) pts had serious AEs. Treatment-related AEs were reported in 13 pts (16%). The most frequent AEs were polyneuropathy (n=10, 12.5%), anemia (n=8, 10%), and fatigue (n=8, 10%). Conclusions: Interim baseline data are as expected for treatment-naïve pts with CD20+ DLBCL; safety results are as expected for rituximab-based treatment. The study is ongoing. [Table: see text]