OBJECTIVES: Trastuzmab for HER2+ metastatic breast cancer (mBC) is available intravenously (TrasIV) and subcutaneously (TrasSC). TrasSC offers time and cost savings under certain conditions. Biosimilar intravenous trastuzumab-dkst (BIOSIMTras) saves costs versus TrasIV and versus TrasSC in some circumstances. We simulated time and costs of BIOSIMTras, reference TrasIV, and TrasSC and modeled budget-neutral expanded access derived from cost savings.

METHODS: Simulations of administration time and drug+administration costs for one MBC patient over one year of monotherapy and one year of Tras+pertuzumab(Per)+paclitaxel(Pac). Using a 2,500-patient-panel with conversion rates from TrasIV/TrasSC to BIOSIMTras from 10-100%, we modeled expanded access to BIOSIMTras using per-label administration times, 3Q2020 average sales price, and 2020 CMS administration reimbursement for 3 patient weights: ptA=56.25kg (25% below-average), ptB=75kg (average), ptC=101.25kg (35% above-average).

RESULTS: In monotherapy, TrasSC saves 85min in cycle 1 and each maintenance cycle (one Q3W cycle versus 3 weekly cycles of TrasIV/BIOSIMTras). BIOSIMTras is cost efficient versus TrasSC in ptA($18,301 savings) and ptB($7,284) and versus TrasIV in all patients with savings up to $27,641 in ptC. Extrapolated to a 2,500-patient-panel, conversion from TrasIV for 1year of monotherapy saves $69,201,460 at 100% in above-avg patients. Conversion from TrasSC at 100% saves $45,752,449 in below-average patients ($18,211,141 in average patients). Savings from conversion from TrasIV could provide up to 39,364 maintenance doses of BIOSIMTras or 1 year of monotherapy to 745 patients (at 100% in above-avg patients). Conversion from TrasSC at 100% could provide 40,282 doses or 764 1-year regimens in below-avg pts. BIOSIMTras+Per+Pac demonstrated savings versus TrasSC in all patients.

CONCLUSIONS: BIOSIMTras monotherapy is cost efficient over TrasIV in all mBC patients and over TrasSC in average and below-average weight patients. BIOSIMTras+Per+Pac is cost efficient over TrasIV and TrasSC in all patients. Savings from conversion to BIOSIMTras can be reallocated—on a budget-neutral basis—to provide expanded access to additional patients or cycles.