SWOG 2308 phase III protocol: Mosunetuzumab vs rituximab for low-tumor-burden FL

Follicular lymphoma (FL) is considered incurable with standard therapies, and current guidelines recommend either active surveillance or rituximab monotherapy for low-tumor-burden FL. However, the availability of immunotherapy options with less toxicity compared to chemotherapy may offer potentially curative treatments in this population.

Mosunetuzumab, a bispecific antibody approved by the FDA for the treatment of FL after two previous therapies, has shown a CMR rate of 87%, translating into improved PFS.¹ Ghosh et al. published the protocol of the phase III SWOG 2308 trial (NCT06337318) evaluating the efficacy and safety of mosunetuzumab vs rituximab for low-tumor-burden FL in the Journal of Clinical Oncology – Oncology Advances.² 

Key learnings

Patients with classical FL, uFL, or dFL by local histology and no previous treatment are eligible. Patients with FL with blastoid, large centrocyte cytologic features or FL Grade 3B are excluded. 

Eligible patients will be randomly assigned (1:1) to receive either rituximab SC, one dose weekly followed by 4 single doses every 8 weeks, or mosunetuzumab SC for 8 cycles once every 21 days.

The primary endpoint is PFS; key secondary endpoints include OS, ORR, and EFS, with a follow-up period of 10 years. The enrollment goal is 540 participants; as of February 14, 2025, 38 participants have been recruited.

If mosunetuzumab shows superior PFS and safety, it could potentially transform the first-line treatment for low-tumor-burden FL, offering a chemotherapy-free option and decreased T-cell exhaustion.