Effectiveness of trastuzumab deruxtecan rechallenge in a patient with HER2-positive metastatic breast cancer: a case report.

Trastuzumab deruxtecan (T-DXd), a high-payload antibody drug conjugate, has been reported to exert potent antitumor effects and has recently shown promising efficacy against human epidermal growth factor receptor 2 (HER2)-positive adenocarcinoma. Despite its high efficacy, interstitial lung disease (ILD) is a severe adverse event (AE) associated with T-DXd. This report describes a patient who was successfully treated with a dose-reduced T-DXd challenge after recovery from ILD. Little disease progression was observed during the treatment interruption period; thus, the effect of T-DXd was considered to have been maintained. T-DXd may induce ILD, and re-administration under careful observation is considered an important option for treating patients with HER2-positive breast cancer.