A Phase 2, Multicenter, Open-Label Trial to Evaluate Efficacy and Safety of Subcutaneous (SC) Mosunetuzumab in Previously Untreated Low Tumor Burden Follicular Lymphoma (LTB-FL).

This is a multi-center, open-label, interventional clinical trial designed to evaluate the efficacy and safety of subcutaneous (SC) Mosunetuzumab as a first-line immunotherapy in patients with low tumor burden follicular lymphoma (LTB-FL), defined by the absence of GELF criteria.

Eligible patients will undergo screening and, upon signing an Informed Consent Form, will receive their first dose of SC Mosunetuzumab.

Mosunetuzumab is administered via SC injection without the need for mandatory hospitalization. The first cycle lasts 21 days, followed by subsequent 28-day cycles. In Cycle 1, Mosunetuzumab is given on Day 1 (5 mg), Day 8 (45 mg), and Day 15 (45 mg). From Cycle 2 onward, a single 45 mg dose is administered on Day 1 of each cycle. Treatment continues for up to 8 cycles (approximately 6 months).

Patients will be monitored for disease status according to standard clinical practice. After completing active treatment, they will enter a post-treatment follow-up phase. Premedication with dexamethasone (20 mg) is mandatory in Cycle 1 and optional in later cycles. Acetaminophen and diphenhydramine may also be administered.

All patients will continue study treatment as per the Schedule of Activities or until premature discontinuation. After treatment discontinuation, disease status assessments will occur approximately every 3 months for up to 24 months. During post-treatment follow-up, PET-CT scans for disease evaluation will be performed every 6 months, as applicable. Patients not under active follow-up will be contacted annually to collect data on disease status and survival.

Throughout the trial, the following data will be collected (as applicable): demographics and baseline characteristics (including sex, age, race, height, and weight), medical history, details of initial diagnosis and treatment history, concomitant medications, adverse events (AEs), serious adverse events (SAEs), disease response, and survival status.