Overall, GHS and quality of life were maintained for both treatment groups, with prespecified PRO variables favouring trastuzumab deruxtecan over treatment of physician’s choice, suggesting that despite a longer treatment duration, there was no detrimental impact on patient health-related quality of life with trastuzumab deruxtecan. When considered with efficacy and safety data from DESTINY-Breast02, these results support the overall benefit of trastuzumab deruxtecan for patients with HER2-positive unresectable or metastatic breast cancer previously treated with trastuzumab emtansine.