GO29781 phase I/II dose expansion: SC mosunetuzumab in R/R FL

Results from the primary analysis of the subcutaneous (SC) cohort (n = 94) of the phase I/II GO29781 study (NCT02500407), evaluating mosunetuzumab in patients with relapsed/refractory (R/R) follicular lymphoma (FL) after ≥2 prior lines of therapy, were published in the American Journal of Hematology by Bartlett et al. The co-primary pharmacokinetic (PK) non-inferiority endpoints were observed Cycle 3 serum trough concentration (C_trough[C3]) and predicted area under the concentration-time curve over 0–84 days (AUC_0–84). Secondary endpoints included complete response (CR) rate, overall response rate (ORR), duration of response (DoR), duration of CR (DoCR), progression-free survival (PFS), and overall survival (OS).

Key data: The geometric mean ratios (GMRs) for C_trough[C3] and AUC_0–84 were 1.39 (90% confidence interval [CI], 1.20–1.61) and 1.06 (90% CI, 0.92–1.21), respectively, demonstrating PK non-inferiority of SC mosunetuzumab to intravenous (IV) administration. The ORR in the SC cohort was 76.6% (95% CI, 66.7–84.7), with 61.7% of patients demonstrating a CR (95% CI, 51.1–71.5). Median DoCR was 34.6 months and median PFS was 23.7 months. Median OS was not reached (NR). Adverse events (AEs) of any grade were reported in 98.9% of patients, with the most common AEs being injection site reactions (60.6%), fatigue (35.1%), cytokine release syndrome (CRS; 29.8%), and diarrhea (20.2%). Grade 3/4 AEs were reported in 48.9% and fatal AEs occurred in 5.3% of patients.

Key learning: SC mosunetuzumab demonstrated non-inferior PK exposure, consistent efficacy, and a manageable safety profile compared with IV administration in patients with R/R FL, potentially offering a more convenient mosunetuzumab administration method in this population.