OBJECTIVES: The aim of this analysis was to assess the cost-effectiveness of Trastuzumab deruxtecan (T-DXd) versus trastuzumab emtansine (T-DM1) in patients with human epidermal growth factor receptor 2 (HER2)-positive unresectable or metastatic breast cancer (uBC/mBC) who have received one prior anti-HER2-based regimen, in Portugal.

METHODS: Based on DESTINY-Breast03 (DB-03) data from May 2021 data cut-off, a 3-state partitioned survival model was developed. For both treatment arms, patients were administered treatment intravenously every 3 weeks until disease progression or withdrawal. The extrapolation of progression-free survival, overall survival and time-to-treatment-discontinuation beyond the trial used log-normal, log-logistic, and log-normal distributions, respectively, for both arms. The model used a three-week cycle length and a lifetime horizon. Costs and healthcare resources utilization estimates were extracted from local databases and published literature. Health utilities for progression-free and progressed-disease health states were sourced from DB-03 data converted to utilities based on Portuguese tariffs, and disutilities for adverse events were based on published literature. Effects were measured in life years (LYs) and quality-adjusted life years (QALYs). Probabilistic and scenario analysis were used to test model assumptions and robustness.

RESULTS: T-DXd was more effective than T-DM1, leading to a mean 1.24 additional LYs (5.78 versus 4.54) per patient. The modeled median percentage of patients alive at 10 years was 24.1% for T-DXd and 15.7% for T-DM1. T-DXd versus T-DM1 was associated with incremental cost-effectiveness ratios (ICER) of 31,086€/LY and 25,260€/QALY, respectively. The probabilistic ICERs were 31,863€/LY and 25,937€/QALY, respectively.

CONCLUSIONS: In this cost-effectiveness assessment designed for the Portuguese setting, T-DXd presented increased costs and increased QALYs compared with T-DM1 for patients with HER2-positive uBC/mBC who had received one prior anti-HER2-based regimen. This cost-effectiveness analysis was considered valid to support the reimbursement decision in Portugal.