Mosunetuzumab with polatuzumab vedotin: Subgroup analyses in patients (pts) with primary refractory or early relapsed large B-cell lymphoma (LBCL).

7021 Background: The primary analysis of mosunetuzumab with polatuzumab vedotin (mosun-pola) in the Phase Ib/II study (NCT03671018) demonstrated durable responses and manageable safety in pts with relapsed or refractory (R/R), transplant-ineligible LBCL (Budde et al. Nat Med 2023). Here, we present results for primary refractory (refr) or early relapse (rel) subgroups from this study after a median follow-up of 23.9 months. Methods: Pts with R/R LBCL (diffuse LBCL not otherwise specified NOS, high-grade B-cell lymphoma HGBCL, transformed follicular lymphoma (FL), and FL grade 3b) and who received ≥1 prior line of therapy (including an anti-CD20 antibody) were treated with mosun-pola. Refr was defined as SD, PD, PR, or CR with relapse <3 months after first-line (1L) therapy. Rel was defined as CR with relapse ≥3 and ≤12 months after 1L therapy. The primary endpoint was best overall response rate (ORR) by IRC using Lugano 2014 response criteria. Key secondary endpoints included CR rate, duration of response (DOR), duration of CR (DOCR), progression-free survival (PFS), overall survival (OS), and safety. Results: As of July 6, 2023, of the 98 pts in the overall population, 45 (46%) and 27 (28%) pts had refr or rel LBCL, respectively. At baseline, the median age in the refr and rel subgroups was 68 and 70 years respectively; 23/45 pts (51%) and 6/27 pts (22%) were treated with mosun-pola as second-line, respectively. The majority of refr/rel pts had DLBCL NOS (71%; 78%) or HGBCL (24%; 19%), Ann Arbor stage III/IV (80%; 89%), elevated LDH (55%; 48%), and extranodal involvement (67%; 59%). In refr pts, the ORR was 49%, which was generally consistent with the overall population (59%); although the sample size was limited, higher responses (ORR: 74%) were observed in rel pts. Additional clinical outcomes are reported (Table). The safety profile was consistent with the overall population. Grade 3 CRS occurred in one pt in each subgroup. Treatment-related ICANS-like events occurred in 2/45 pts (4%; refr) and 3/27 pts (11%; rel). Conclusions: Mosun-pola demonstrated durable benefits in ORR and CR rates irrespective of a poor response to 1L treatment. Outcomes for pts with refr or rel LBCL are encouraging. Clinical trial information: NCT03671018 . Table: see text