OBJECTIVES: Breast cancer is estimated to have the highest incidence among all cancers in the United States (US) in 2020. In turn, the incidence of gastric cancer is ranked fifteenth among all cancers in the US. Targeted therapies, such as trastuzumab, have drastically improved clinical outcomes for patients with over-expressive human epidermal growth factor receptor 2 (HER2+) in early-stage breast cancer (EBC) and metastatic breast cancer (MBC) as well as metastatic gastric cancer (MGC). However, due to the high cost of treatment and eligible patient population size, originator trastuzumab has caused patient affordability challenges and represents a high budget burden on payers. The objective of this study is to assess the potential financial impact associated with the use of intravenous (IV) trastuzumab biosimilar Ontruzant compared to the originator, in patients with HER2+ EBC, MBC and MGC from the US healthcare payer perspective. METHODS: A budget impact model with a 5-year time horizon was developed to compare costs ($; 2020) under scenarios with and without the entry of Ontruzant to a healthcare plan. Only direct costs were considered following a payer perspective. Drug acquisition costs were estimated based on the published wholesale acquisition cost (WAC) price. The target population consisted of incident HER2+ patients eligible to receive trastuzumab IV or subcutaneous. Epidemiological data were obtained from SEER database and Epic Oncology. Predictions on trastuzumab market share and Ontruzant uptake were based on internal market research. The model calculated the budget impact of Ontruzant by indication and across all indications. RESULTS: In a hypothetical healthcare plan with one million members, the number of incident patients treated with the trastuzumab class was estimated to range from 107 in year 1 to 100 in year 5 in HER2+ EBC and 17 to 16 in HER2+ MBC. About ten new patients with HER2+ MGC were estimated to be treated with trastuzumab or biosimilars each year in year 1 to 5. The market uptake of Ontruzant with the trastuzumab class was assumed 50% in year 1 and rising over time to 90% in year 5, which led to a total budget saving of $13,534,498 in EBC and MBC and $459,331 in MGC over the 5-year period for the healthcare plan. The model yielded an average saving of $1,859, $2,073 and $766 per treated member per month in EBC, MBC and MGC, respectively. The cost saving was mainly driven by the lower drug acquisition cost of Ontruzant compared to originator trastuzumab, as well as potential reduction of vial wastage due to the availability of Ontruzant multi-dose vials. CONCLUSIONS: Adding Ontruzant to the formulary for treatment of HER2+ breast cancer and gastric cancer and creating mechanisms to encourage providers to utilize Ontruzant instead of the reference branded agent, could lead to substantial cost-savings for the US healthcare payers; and consequently, improve access to treatments for the patients.

Citation Format: Min Huang, Puneet Singhal, Reshma Shinde, Sarah K Wilkes, Nirav Nagda, Yunni Yi, Stefano Lucherini. Budget impact of Ontruzant for the treatment of breast cancer and gastric cancer in the United States [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS9-68.