Background: The combination of Pola-R-Len may enhance anti-tumor response in R/R DLBCL. We report the primary analysis of the R/R DLBCL cohort in a Phase 1b/2 study (GO29834; NCT02600897). Methods: Pts received induction with 6 x 28-Day (D) cycles (C) of: Pola 1.8mg/kg intravenous (IV; C1−6: D1); R 375mg/m² IV (C1−6: D1) and oral Len 10–20mg (dose escalation) or recommended Phase 2 dose (RP2D) daily on D1–21. Pts with a response at end of induction (EOI) received 6 months (mo) consolidation with R 375mg/m² (D1 every 2 mo) and Len 10mg (D1–21 monthly). Primary endpoints were safety/tolerability and positron emission tomography (PET)-complete response (CR) rate at EOI by independent review committee (IRC) by modified Lugano criteria. Results: At primary analysis (Sep 08, 2020), 57 pts were enrolled. Median age was 71 years (range 28–92); male (67%); Ann Arbor Stage III–IV (86%); International Prognostic Index 3–5 (60%); median 2 prior therapies; prior bone marrow transplant (11%); prior CAR-T therapy (5%); primary refractory (49%) and refractory to last therapy (65%). Grade 3–4 adverse events (AEs) were experienced by 75% of pts, most commonly, neutropenia (58%), thrombocytopenia (14%), infections (14%) and anemia (11%). AEs led to Len dose reduction in 25% and interruption in 63% of pts. One Grade 5 treatment-related AE (neutropenic sepsis) was reported. In total, 49 pts were treated at RP2D (Pola 1.8mg/kg + Len 20mg). IRC PET-CR rate at EOI was 29% (Table). A best overall response (BOR) assessed by investigator (INV) was seen in 36/49 (74%) pts with 17/49 (35%) pts achieving a CR; of these, 14/17 (82%) remain in remission at the cutoff date. Median duration of response (DOR) was 8.1 mo (95% confidence interval [CI]: 4.7–not evaluable [NE]). After a median follow-up of 9.7 mo, median progression-free survival (PFS) and overall survival (OS) were 6.3 mo (95% CI: 4.5–9.7) and 10.9 mo (95% CI: 7.4–NE), respectively. Conclusions: Our study of the novel triplet combination, Pola-R-Len, demonstrates a tolerable safety profile. This first efficacy report of Pola-R-Len shows promising activity in a difficult-to-treat R/R DLBCL population, particularly in pts achieving CR, a large proportion of whom remain in remission at the cutoff date. Further evaluation of Pola-R-Len and the impact of consolidation therapy is warranted to address the significant unmet need in this patient population. Clinical trial information: NCT02600897

*Primary efficacy endpoint; ^†Defined as best response of CR or partial response during the study. ORR, overall response rate.