Mosunetuzumab monotherapy was associated with clinically meaningful outcomes in patients with relapsed/refractory (R/R) follicular lymphoma (FL), according to a follow-up report from a pivotal phase 2 trial. Results were presented in a poster at the SOHO 2023 Annual Meeting by Nancy L. Bartlett, MD, of the Siteman Cancer Center at the Washington University School of Medicine in St. Louis, Missouri, and colleagues.

The single-arm, multicenter, pivotal phase 2 study ( Identifier: NCT02500407) enrolled patients with FL of grade 1 to 3a, an Eastern Cooperative Oncology Group performance status of 0 or 1, and a history of 2 or more prior therapies. Prior treatment needed to include an anti-CD20 antibody and an alkylator.

In this study, mosunetuzumab was administered intravenously in 21-day cycles using step-up dosing in cycle 1. Patients received 8 cycles if they reached complete response (CR) by cycle 8, while patients in partial response (PR) or stable disease by cycle 8 received 17 cycles.

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The study had previously met its primary endpoint based on analysis of the CR rate, so in their poster the research team presented updated results with an additional 10 months of study follow-up.

There were 90 patients enrolled in the study, with a median age of 60 years (range, 29-90). Patients had a median of 3 lines of prior therapy (range, 2-10), and most patients (77%) had stage III or IV disease. The median follow-up time was 28.3 months, with 62% of patients having completed therapy.

With mosunetuzumab monotherapy, the objective response rate in this study was 78% (95% CI, 68%-86%), and the CR rate was 60% (95% CI, 49%-70%). The median duration of response was not reached, and the median duration of CR was also not reached.

The median progression-free survival (PFS) time was 24 months (95% CI, 12-not reached). The study investigators considered results for response rates, median duration of CR, and PFS to be improved with mosunetuzumab in comparisons with patients’ last prior therapy.

The researchers indicated there have were no new grade ≥3 adverse events (AEs), serious AEs, or treatment-related AEs reported with the additional follow-up. They also indicated that all cytokine-release syndrome (CRS) events had been resolved by the time of the current report and that there had been no new CRS events reported with additional follow-up.

The study investigators concluded that in this study of heavily pretreated patients with R/R FL, clinically meaningful outcomes were seen with mosunetuzumab after more than 2 years of follow-up. They also considered the safety profile of this agent to be manageable.

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, or device companies. Please see the original reference for a full list of disclosures.


Bartlett NL, Sehn LH, Matasar M, et al. Mosunetuzumab monotherapy demonstrates durable efficacy with a manageable safety profile in patients with relapsed/refractory follicular lymphoma who received ≥2 prior therapies: updated results from a pivotal phase II study. Presented at: the Eleventh Annual Meeting of the Society of Hematologic Oncology (SOHO); September 6-9, 2023. Abstract IBCL-458.