OBJECTIVES: By September 8, 2022, 10 biological monoclonal antibody (mAb) biosimilar products for cancer treatment had been approved and marketed in the United States (U.S.). These biosimilars were approved based on bioequivalence studies conducted among healthy volunteers, but their post-marketing investigations for safety are limited. This research aims to examine adverse event (AE) reporting patterns and disproportionate reporting signals for mAb biosimilars in the U.S. compared to their originator biologics.

METHODS: The U.S. Food and Drug Adverse Event Reporting System database (January 1, 2004–December 31, 2021) was used to identify AE reports for Rituxan®, Avastin®, Herceptin®, and their biosimilars. Proportions of patient age and sex, as well as type of reporters of AEs were described for these reports. Reporting odds ratios (RORs) with 95% confidence intervals (CIs) were calculated to compare reporting disproportionality in serious, death, and specific AEs between mAb biologics/biosimilars (index) and all other drugs. Breslow-Day statistic was used to determine homogeneity in RORs between each mAb biologic–biosimilar pair at p<0.05.

RESULTS: A total of 48,691 AE reports for these products were identified. Among identified AE reports, 2,219 (4.6%) were related to biosimilars and the rest were for biologics. Missing information of age and sex existed across all AE reports with studied mAb biologics and biosimilars. More AEs for all biologics, as well as Avastin® and Herceptin® biosimilars, were reported by health professionals, while consumers were the highest proportion of reporters for Rituxan® biosimilars (67.3%). We observed no risk signals of serious or death AE reporting for all three mAb biosimilars. However, a signal of disproportionate reporting of death was detected between Avastin® and its biosimilars.

CONCLUSIONS: Our findings support the similarity in signals of disproportionate AE reporting between mAb originator biologics and biosimilars, except for death between Avastin® and its biosimilars.