OBJECTIVES : To compare cost-efficiency and budget-neutral expanded access of biosimilar trastuzumab-dkst intravenous (IV) achieved through conversion from trastuzumab subcutaneous (SC) in metastatic breast cancer in the United States (US) and France.

METHODS : Model inputs included: a panel of 1000 female patients; three weight (W) categories (US: W1: 62.2kg; W2: 73.1kg; W3: 88.6kg; France: W1: 49.5kg; W2: 66kg; W3: 82.5kg); conversion rates of 10-100%; drug costs (US: Average Selling Price [US$]; France: Public Unit Price [€] converted to US purchasing power parity [US$PPP]); drug administration costs; one year of trastuzumab-SC (Q3 weeks) vs trastuzumab-dkst IV (weekly) monotherapy and in combination with pertuzumab (Q3 weeks IV and SC).

RESULTS : Cost-savings of trastuzumab-dkst over trastuzumab-SC monotherapy range from $564,347 (W3 at 10% conversion) to $20,706,175 (W1 at 100%) in the US and from $1,465,126 (W3;10%) to $25,438,492 (W1;100%) in France. In combination with pertuzumab, trastuzumab-dkst saves up to $34,234,181 (W1;100%) in the US and up to $27,610,228 (W1;100%) in France. In the US, reallocation of these savings can provide between 425 (W3;10%) and 19,810 (W1;100%) additional maintenance doses of trastuzumab-dkst monotherapy, sufficient to treat 8 to 376 patients, respectively, for one year. In France, these savings can provide between 2,606 (W3;10%) and 70,932 (W1;100%) additional maintenance doses or 49 to 1342 one-year treatment regimens, respectively. For trastuzumab-dkst in combination with pertuzumab, savings could expand access to 202 (W3;10%) to 4,379 (W1;100%) additional maintenance doses or 11 (W3;10%) to 232 (W1;100%) one-year regimens in the US; in France, savings can provide between 254 (W3;10%) and 4728 (W1;100%) additional maintenance doses or 13 (W3;10%) to 243 (W1;100%) one-year regimens.

CONCLUSIONS : Trastuzumab-dkst monotherapy and combination therapy are cost-efficient versus trastuzumab-SC in the US and France. Cost-savings can be reallocated on a budget-neutral basis to expand access to additional maintenance doses and one-year regimens of trastuzumab-dkst.