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The FDA to the bispecific monoclonal antibody mosunetuzumab (Lunsumio) for relapsed/refractory follicular lymphoma after two or more prior lines of therapy.

A first-in-class cancer immunotherapy, the drug works by inducing CD20-directed CD3 T-cell engagement. Accelerated approval comes with a requirement for additional studies to provide confirmatory evidence of a drug's safety and efficacy.

"This approval is a significant milestone for people with relapsed or refractory follicular lymphoma, who have had limited treatment options until now," said Elizabeth Budde, MD, PhD, of City of Hope in Duarte, California, in a from Genentech. "As a first-in-class, T cell-engaging bispecific antibody that can be initiated in an outpatient setting, Lunsumio's high response rates and fixed-duration could change the way advanced follicular lymphoma is treated."

Support for the contingent approval status came from the phase II GO29781 trial involving 90 patients who had progressive follicular lymphoma after at least two prior therapies, including an anti-CD20 monoclonal antibody and an alkylating agent. The primary analysis showed that mosunetuzumab achieved objective responses in 80% of the study population, including complete responses in 60%. After a median follow-up of 14.9 months, responding patients had a median duration of response of 22.8 months. Estimated response rates at 12 and 18 months were 62% and 57%, respectively.

Prescribing information for mosunetuzumab includes a boxed warning about a potential for serious or life-threatening cytokine release syndrome (CRS). In a pooled safety analysis of 218 patients treated with the recommended dose of the bispecific antibody, CRS occurred in 39%, neurologic toxicity in 39%, serious infections in 17%, and tumor flare in 4%. Grade 3 CRS occurred in 2% of patients and grade 4 in 0.5%.

The most common (≥20% of patients) adverse events (AEs) of any grade were CRS, fatigue, rash, pyrexia, and headache. The most common grade 3/4 laboratory abnormalities (≥10%) were decreased lymphocytopenia, hypophosphatemia, hyperglycemia, neutropenia, hyperuricemia, leukopenia, decreased hemoglobin, and anemia.

As an off-the-shelf product, mosunetuzumab is ready to use, avoiding delays in treatment associated with certain cellular therapies for hematologic malignancies, notably CAR T-cell therapy. Treatment can be administered as an outpatient infusion, although hospitalization might be required to manage certain AEs, according to Genentech. Additional studies of the bispecific antibody include evaluation of a subcutaneous formulation.

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