Background: Biosimilar trastuzumab (trastuzumab-qyyp) was the fourth trastuzumab biosimilar in Europe in 2018. The objectives of this study were to understand the utilization of biosimilar trastuzumab and its benefits and risks in a real-world setting.

Materials and methods: In this observational study, patients in the Netherlands and Norway treated with biosimilar trastuzumab for early stage (stage 0-3) HER2+ breast cancer were recruited (February 2020-July 2021). Data recorded were biosimilar trastuzumab treatment patterns, patient demographics, clinical characteristics, tolerability, and healthcare resource utilization (HCRU).

Results: 102 patients were included; 74 (72.6%) received initial treatment with biosimilar trastuzumab, 26 (25.5%) switched from originator, and 3 (2.9%) switched from other trastuzumab biosimilars. The median (Q1-Q3) biosimilar trastuzumab initial dose was 8.0 mg/kg (6.0-8.0). Dose change occurred in 78 (76.5%) patients. Patients received biosimilar trastuzumab treatment for a mean (SD) of 245.6 (107.2) days. Biosimilar trastuzumab was part of combination therapy in 100 patients (98.0%)—38 (37.2%) combination regimens included platinum-based drugs and 40 (39.2%) combination regimens included pertuzumab. A total of 48 patients discontinued or switched due to tolerability (22.9% of N=48), lack of response (4.2%), patient preference (4.2%), dosing schedule (22.9%), and other (43.8%). A total of 66 adverse events occurred and 4 were severe (one case of each: acute pericarditis, recurrent acute pericarditis, recurrent pericarditis, and severe cardiac toxicity). Treatment was stopped due to heart monitoring findings in one patient. Over half of patients were hospitalized for a mean (SD) 7.7 (42.6) days due to breast cancer surgery including reconstructions (32.7%), PICC line/port-a-cath procedures (15.8%), fever (13.9%), ablation (5.9%), and other unspecified surgery (5.9%).

Conclusions: Switching between reference product and biosimilar and use of biosimilar trastuzumab combination regimens are being adopted in real-world oncology practice. Treatment patterns and tolerability were consistent with the product label. HCRU was high in this population.