The FDA’s decision to approve mosunetuzumab marks the first bispecific antibody approved to treat follicular lymphoma.
The FDA has approved mosunetuzumab-axgb (Lunsumio) for patients with relapsed/refractory follicular lymphoma after 2 prior lines of therapy, according to a press release from Genentech.1
The complete response (CR) rate based on an independent review facility (IRF) was 60% (95% CI, 49%-70%), and the objective response rate (ORR) was 80% (95% CI, 70%-88%).
Additionally, the investigator assessed CR rate was 60% (95% CI, 49%-70%) and the ORR was 78% (95% CI, 68%-86%). The concordance rates for CR and ORR for IRF vs investigator assessment was 93% and 96%, respectively.
“This additional treatment option is good news for people whose blood cancer has not responded to multiple lines of treatment because it can become more difficult to treat each time it returns,” Lee Greenberger, PhD, chief scientific officer of the Leukemia & Lymphoma Society, said in the press release. “This bispecific antibody is an off-the-shelf, accessible treatment option that has the potential to help those with relapsed or refractory follicular lymphoma achieve remission.”
The approval was based on results from the phase 1/2 GO29781 trial (NCT02500407). Results of the study were previously presented at the 2021 American Society of Hematology (ASH) Annual Meeting, and focused on mosunetuzumab monotherapy.2
Most recently, findings from an updated analysis presented at the 2022 ASH Annual Meeting confirmed that treatment with mosunetuzumab elicited durable response rates and was associated with a low rate of adverse events after treatment was stopped.3
At the time of the study’s read out, a total of 90 patients in each arm were enrolled in the trial. Patients were given mosunetuzumab every 3 weeks intravenously with step-up dosing beginning in cycle 1.
Patients received 8 cycles if a complete response (CR) was achieved after cycle 8, and 17 cycles were given if a partial response or stable disease were observed after cycle 8. On day 1, cycle 1, patients received 1 mg followed by 2 mg on day 8 and 60 mg on day 15. In cycle 2 patients started with 60 mg, cycle 3 began with 30 mg, and cycles 8 to 17 started at 30 mg.
The study’s primary end point was CR as a best response, with secondary end points being overall response rate (ORR), duration of response (DOR), safety, and tolerability.
Patients had a median age of 60 years and 61.1% were male. Additionally, 58.9% had an ECOG performance status of 0. Patients received a median number of 3 lines of therapy.
Investigators reported that 53.3% of patients were refractory to any prior CD20 therapy and alkylator therapy, and 52.2% had progression of disease up to 24 months (POD24). The median follow-up was 18.3 months, and 58.9% received 8 cycles of prior treatment.
The CR rate in patients who were double refractory was 50% (95% CI, 35%-65%) vs 71% (95% CI, 55%-84%) in those who were not. Among those who had POD24, the CR rate was 57% (95% CI, 42%-72%) and 63% (95% CI, 47%-77%) for those who did not.
Patients who were double refractory also achieved an ORR of 71% (95% CI, 56%-83%) vs 90% (95% CI, 77%-97%) among those who were not. Additionally, ORR for those with POD24 was 85% (95% CI, 72%-94%) vs 74% (95% CI, 59%-86%) for those who were not.
The median DOR in responders was 22.8 months (95% CI, 9.7-not evaluable [NE]), with a median time to first response of 1.4 months. Moreover, the 12-month event-free rate (EFS) was 62% (95% CI, 50%-74%) and the 18-month rate was 57% (95% CI, 44%-70%).
For complete responders, the median DOR was 22.8 months (95% CI, 18.7-NE), with a median time to first CR of 3.0 months. Additionally, the 12-month EFS was 76% (95% CI, 65%-88%) and the 18-month rate was 70% (95% CI, 57%-84%).
The median progression-free survival was 17.9 months (95% CI, 10.1-NE).
Grade 3/4 adverse effects (AEs) occurred in 70.0% of patients, 51.1% of which were related to mosunetuzumab treatment. Serious AEs were observed in 46.7% of patients, 33.3% of which were mosunetuzumab-related, and there were 2.2% that were grade 5 AEs, but none were related to mosunetuzumab. Discontinuation of treatment because of AEs occurred in 4.4% of patients, 2.2% of which were mosunetuzumab-related.
Grade 3/4 cytokine release syndrome (CRS) occurred in 2 patients, respectively. The median duration of CRS was 3 days. Treatment of corticosteroids was necessary in 11.1% of patients and tocilizumab (Actemra) was used in 7.8%.
Other AEs of special interest included grade 3/4 neutropenia in 26.7%, serious infection in 14.4%, and immune effector cell–associated neurotoxicity syndrome in 4.4%.
Previously, mosunetuzumab had been granted priority review by the FDA in July 2022 for patients with relapsed/refractory follicular lymphoma after 2 or more prior systemic therapies.4
“This approval is a significant milestone for people with relapsed or refractory follicular lymphoma, who have had limited treatment options until now,” Elizabeth Budde, MD, PhD, a hematologic oncologist and associate professor in the Division of Lymphoma at City of Hope, said in the release. “As a first-in-class T-cell engaging bispecific antibody that can be initiated in an outpatient setting, [mosunetuzumab’s] high response rates and fixed-duration could change the way advanced follicular lymphoma is treated.”