Additional follow-up data from the phase 2 MorningSun study showed a 91.9% overall survival rate for previously untreated patients with high-tumor burden follicular lymphoma who received subcutaneous mosunetuzumab with optional maintenance therapy.
The 12-month follow-up results were presented by John M. Burke, MD, of the Rocky Mountain Cancer Center in Aurora, Colorado, during the 67th ASH Annual Meeting and Exposition.
Intravenous mosunetuzumab, a CD20×CD3 bispecific antibody, is FDA-approved for the treatment of relapsed/refractory FL.
This analysis is assessing the SC formulation of mosunetuzumab in treatment-naïve patients with high-tumor burden FL. A total of 103 patients (median age, 65 years; 51.5% female; 91.3% with Ann Arbor stage III/IV disease) received step-up dosing during cycle one (day [D] 1, 5 mg; D8, 45 mg; D15, 45 mg) followed by 45 mg on D1 of each 21-day cycle for up to one year. Patients with partial or complete metabolic response (CMR) could continue mosunetuzumab maintenance 45 mg every 8 weeks for up to 1 year.
More than half of patients (n=69) completed the full 17 cycles of treatment, 46 of whom received maintenance therapy.
The overall response rate was 87.4%, including 64.1% in CMR. Twelve-month outcomes included:
- Progression-free survival rate: 85.5%
- Duration of response: 89.6%
- Duration of complete response: 91.1%
No patients who underwent maintenance experienced disease progression. One patient died.
The most common adverse events patients experienced were:
- Injection-site reaction: 67.0%
- Fatigue: 44.7%
- Cytokine release syndrome (CRS): 34.0%
- Headache: 32.0%
- Nausea: 32.0%
Grade 3 adverse events were reported in 47.6% of patients, and serious adverse events were reported in 36.9% of patients. Most patients (77.7%) experienced infections, the most common of which was COVID-19 (24.3%).
Most patients in the maintenance cohort (80.4%) experienced adverse events, though CRS did not occur in this cohort. Nearly half of patients (45.7%) had infections during maintenance phase.
Among 22 patients with available ctDNA data, 86.4% (n=19) were measurable residual disease-negative, “thus supporting the fixed treatment duration of mosunetuzumab SC,” the authors noted.
“These data support the outpatient administration of mosunetuzumab SC in US community practices and further evaluation of mosunetuzumab-based treatment in first-line [high-tumor burden] FL,” the authors concluded.
Reference
Burke JM, Sharman J, Anz B, et al. Fixed-duration subcutaneous (SC) mosunetuzumab, with maintenance therapy, in patients (pts) with previously untreated high-tumor burden follicular lymphoma (HTB FL): longer follow-up and exploratory circulating tumor (ct)DNA analysis of the phase II MorningSun study. Abstract #4494. Presented at the 67th American Society of Hematology Annual Meeting and Exposition; December 6-9, 2025; Orlando, Florida.
