BACKGROUND: Trastuzumab is an antihuman epidermal growth factor receptor 2 monoclonal antibody used to treat breast and other cancers. Trastuzumab biosimilars were approved in the United States beginning in 2017. Utilization information on these biosimilars is limited. OBJECTIVE: To examine utilization patterns and characteristics of patients treated with trastuzumab (biosimilars and reference) and other human epidermal growth factor receptor 2 products. METHODS: We evaluated health care claims data from the Biologics and Biosimilars Collective Intelligence Consortium distributed research network, representing a large, geographically diverse US population of commercially insured individuals. We queried 4 distributed research network health plan partners to capture product usage data and patient information from October 1, 2016, to October 31, 2022. Patients were required to be continuously enrolled in their health plan for at least 365 days before their first observed trastuzumab utilization date in this study period. Data were aggregated across data partners. RESULTS: More than 16 million eligible health plan members representing more than 31 million person-years of data were evaluated. We identified 5,984 incident treatment episodes; 3,878 (64.8%) episodes were with the reference trastuzumab. The mean ages were consistent across trastuzumab products (60.2 to 65.1 years) and at least 80% of the episodes were among female patients. The mean comorbidity index score was 1.2 (SD = 1.9) among users of the reference vs the biosimilars (range 1.2-2.5). Other clinical characteristics (eg, diabetes, hypertension) were comparable across products. The proportion of total incident episodes of the reference trastuzumab decreased substantially over time (96% in 2016 vs 28% in 2021) as utilization of the biosimilars increased (eg, use of trastuzumab-anns increased from 2% [2019] to 36% [2021]). Similar utilization trends were seen among patients with and without metastatic breast cancer. CONCLUSIONS: Trastuzumab biosimilars utilization has grown since their introduction to the US market. Exploration of these biosimilars' comparative effectiveness and safety to their reference product is warranted.