ERBB2 and breast cancer: For all HER2-Low advanced BC patients (Scenario 1), HER2+ advanced BC patients (Scenario 2), and HER2- advanced BC patients (Scenario 3), T-DXd was cost-effective at a WTP threshold of $50,000/QALY with a price of less than $17.00/mg, $17.13/mg, $14.07/mg, respectively (S3 Fig).