Real-world safety profile of mosunetuzumab: a pharmacovigilance study based on the food and drug administration adverse event reporting system

Background Mosunetuzumab is a CD20×CD3 bispecific antibody approved for adult relapsed or refractory follicular lymphoma. Post-marketing evidence on its safety profile remains scarce. This pharmacovigilance study used the Food and Drug Administration Adverse Event Reporting System (FAERS)to characterize real-world adverse event (AE) signals associated with mosunetuzumab. Methods We performed disproportionality analysis using reports from the FAERS database spanning from the first quarter of 2004 to the fourth quarter of 2025. The primary analysis set encompassed reports wherein mosunetuzumab was coded as the Primary Suspect (PS). Disproportionality analyses were performed using four algorithms: reporting odds ratio (ROR), proportional reporting ratio (PRR), Bayesian confidence propagation neural network (BCPNN), and multi-item gamma poisson shrinker (MGPS). After excluding implausible records, the time to onset (TTO)for AEs was summarized using the median and interquartile range. Results Overall, 1154 FAERS reports mentioning mosunetuzumab were included in the primary analysis. 3 positive signals were identified at the System Organ Class (SOC)level. Cytokine release syndrome (CRS), neutropenia, tumour flare and infection-related events were frequently reported signals at the Preferred Term (PT)level. Additional disproportionate reporting signals were noted for cardiac events and eye disorders, including atrial fibrillation, uveitis. Of 310 reports with valid dates, most AEs occurred within 30 days following treatment initiation, whereas a nontrivial proportion was reported at ≥180 days. Conclusion This study offers real-world evidence for guiding the clinical use of mosunetuzumab. It highlights the necessity for clinicians to monitor for AEs during treatment by recognizing potential adverse reaction signals beyond those documented in the current prescribing information.