Tazemetostat and Mosunetuzumab in Untreated Follicular Lymphoma

This is a phase II, open-label study. Fifty patients will be enrolled and treated with standard dosing of SC mosunetuzumab, and with oral tazemetostat by mouth twice daily at standard dosing (800 mg twice daily) beginning at the same time as mosunetuzumab initiation. Response assessments by PET/CT will occur post-mosunetuzumab at Cycle 4, Day 1 (+/- 3 days) and again at the end of treatment. If a participant has a complete response (CR) at Cycle 4 and/or cycle 8, then they will receive a total of 8 cycles of mosunetuzumab. If the patient has a partial response or stable disease at Cycle 4 and Cycle 8, then they will receive a total of 12 cycles of mosunetuzumab. All participants will receive 12 cycles of tazemetostat, unless discontinued from treatment early for disease progression or other protocol-defined reasons. Treatment with steroids, tocilizumab, growth factors, tumor lysis prophylaxis, and antibiotics may be used as per standard of care at our institution. Dose modifications are permitted for toxicity. Correlative studies will be performed prior to and following tazemetostat treatment and peripheral blood collections prior to post-mosunetuzumab treatment, which will give additional descriptive data for use in correlative analyses.