Subcutaneous Mosunetuzumab Demontrates Promising Efficacy in Previously Untreated High-Tumor Burden FL
Fixed-duration subcutaneous (SC) mosunetuzumab demonstrated promising efficacy and a manageable safety profile in patients with previously untreated high–tumor burden follicular lymphoma (FL), according to interim results from the phase 2 MorningSun trial.
These data will be presented by Ian Flinn, MD, Tennessee Oncology and OneOncology, Nashville, Tennessee, at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago, Illinois.
Mosunetuzumab is a CD20-CD3 bispecific antibody currently approved for relapsed/refractory FL after at least 2 prior lines of therapy. In this cohort of the MorningSun study, investigators evaluated its fixed-duration SC formulation in the frontline setting for patients with high–tumor burden FL. The treatment regimen consisted of step-up dosing in cycle 1 (5 mg on day 1; 45 mg on days 8 and 15) followed by 45 mg SC on day 1 of each 21-day cycle for up to 17 cycles. Corticosteroid prophylaxis was mandated in the first 2 cycles to mitigate cytokine release syndrome (CRS).
The primary end point was progression-free survival at 24 months. Secondary end points were objective response rate (ORR), time to response (TTR), and safety.
Overall, 102 patients were enrolled, of which 55 patients completed initial treatment and 16 remained on active treatment. Maintenance therapy was initiated by 42 patients who achieved partial or complete metabolic response (CMR) following initial treatment. The median age was 65 years and 52% of patients were female.
The median duration of follow-up was 13.9 months and the 12-month PFS rate was 82.8% (95% confidence interval [CI], 73.0 to 89.3). The median TTR was 2.7 months (range, 1.2 to 5.8). The ORR was 87.3% and 60.8% of patients achieved CMR.
In terms of safety, the most common adverse events were injection-site reactions (57.8%), fatigue (42.2%), CRS (34.3%), headache (31.4%), and nausea (30.4%). Grade 3 or higher adverse events were reported in 44.1% of patients and serious adverse events were reported in 29.4% of treated patients. Grade 1 CRS was reported in 29.4% of patients and grade 2 CRS was reported in 4.9% of patients.
“Mosunetuzumab SC demonstrated promising efficacy in patients with previously untreated high-tumor burden FL. The manageable safety profile, including rate of CRS, supports the administration of fixed duration mosunetuzumab SC in an outpatient setting. Additional data, including cytokine profiling and T/B/NK dynamics, will be presented,” the researchers concluded.
Source:
Flinn I, Sharman J, Anz III B, et al. Fixed duration subcutaneous (SC) mosunetuzumab (Mosun) in patients with previously untreated high-tumor burden follicular lymphoma (FL): Interim results from the phase II MorningSun study. Presented at 2025 ASCO Annual Meeting. May 30-June 3, 2025; Chicago, IL. Abstract 7014.
