Glofitamab Monotherapy in Relapsed or Refractory Large B-Cell Lymphoma: Extended Follow-Up from a Pivotal Phase II Study and Subgroup Analyses in Patients with Prior Chimeric Antigen Receptor T-Cell Therapy and by Baseline Total Metabolic Tumor Volume

Background: Glofitamab is a CD20xCD3 bispecific antibody with a 2:1 (CD20:CD3) format that engages and redirects T cells to eliminate B cells. In a pivotal Phase II study (NCT03075696), fixed-duration glofitamab monotherapy induced high complete response (CR) rates and had a manageable safety profile in patients with relapsed and/or refractory (R/R) large B-cell lymphoma (LBCL; Dickinson et al. N Engl J Med 2022). Here, we present an extended follow up, as well as subgroup analyses in patients with prior chimeric antigen receptor (CAR) T-cell therapy and by baseline total metabolic tumor volume (TMTV). Methods: Patients with LBCL and ≥2 prior therapies received obinutuzumab pretreatment (1000mg) on Day (D) 1 of Cycle (C) 1. Intravenous glofitamab was then given as step-up doses during C1 (2.5mg on D8; 10mg on D15), followed by the target dose (30mg) on D1 of C2-12 (21-day cycles; total of 8.3 months). The primary endpoint was independent review committee (IRC)-assessed CR rate using Lugano criteria (Cheson et al. J Clin Oncol 2014). Cytokine release syndrome (CRS) events were assessed using American Society for Transplantation and Cellular Therapy criteria (Lee et al. Biol Blood Marrow Transplant 2019). Exploratory analyses were performed to investigate the association between TMTV at baseline and progression-free survival (PFS) and CRS. As there is currently no consensus on the method for standardized uptake value (SUV) thresholding in non-Hodgkin's lymphoma, a variety of methods are used in clinical studies (Keijzer et al. Comput Struct Biotechnol J 2023). Here, we used IRC-assessed TMTV derived from baseline positron emission tomography images using a semi-automatic method with a threshold for TMTV of 2x the SUV mean of the liver. Results: As of May 1, 2023, 155 patients were enrolled; 154 patients had received ≥1 dose of study treatment. Baseline characteristics were as previously presented (Dickinson et al. N Engl J Med 2022): median prior therapies received was 3 (range: 2-7); 33% of patients had received prior CAR T-cell therapy, and 85% were refractory to their most recent regimen. Median time on study was 25.8 months (range: 0-35). The IRC-assessed overall response and CR rates were 52% and 40%, respectively. The majority of CRs (40/62; 65%) were ongoing at data cut-off. Median duration of CR (DoCR) was 26.9 months (95% confidence interval [CI]: 18.4-not evaluable [NE]); an estimated 67% of patients with a CR at any time remained in remission at 1