Key model inputs.

Objective
The clinical efficacy and safety profile of trastuzumab deruxtecan (T-DXd) have been demonstrated in previously treated patients with human epidermal growth factor receptor 2 (HER2)-low advanced breast cancer (BC). It is, however, necessary to evaluate the value of T-DXd considering both its clinical efficacy and its cost, given that it is high. This study aimed to evaluate the cost-effectiveness of T-DXd versus chemotherapy in patients with previously treated HER2-low advanced BC.
Methods
We used a partitioned survival model that included three mutually exclusive health states. The patients in the model were identified based on their clinical characteristics and outcomes from the DESTINY-Breast04. Probabilistic and one-way sensitivity analyses were performed to evaluate the model’s robustness. Subgroup analyses were also conducted. The measures included costs, life years, quality-adjusted life-years (QALYs), incremental cost-effectiveness ratios (ICERs), incremental net health benefits (INHBs), and incremental net monetary benefits (INMBs).
Results
The ICERs of T-DXd vs. chemotherapy were $83,892/QALY, $82,808/QALY, and $93,358/QALY in all HER2-low advanced BC patients, HER2-positive (HER2+) advanced BC patients and HER2-negative (HER2-) advanced BC patients, respectively. In one-way sensitivity analysis, the cost of T-DXd and hazard ratio (HR) for progression-free survival (PFS) and overall survival (OS) were also identified as key drivers. If the price of T-DXd decreased to $17.00/mg, $17.13/mg, and $14.07/mg, it would be cost-effective at a willingness to pay (WTP) threshold of $50,000/QALY in all HER2-low advanced BC patients, HER2+ advanced BC patients and HER2- advanced BC patients, respectively. At a WTP threshold of $100,000/QALY, the probability of T-DXd being cost-effective was 81.10%, 82.27%, and 73.78% compared to chemotherapy for all HER2-low advanced BC patients, HER2+ advanced BC patients and HER2- advanced BC patients, respectively. Most subgroups of patients with HER2+ disease had a cost-effectiveness probability of > 50%.
Conclusion
From a third-party payer’s perspective in the United States, the findings of the cost-effectiveness analysis revealed that, at the current price, T-DXd is a cost-effective alternative to chemotherapy for patients with prior HER2-low advanced BC, at WTP threshold of $100,000/QALY.