Idiosyncratic Drug-Induced Liver Injury and Trastuzumab Deruxtecan in Breast Cancer: A Case Report.

Trastuzumab deruxtecan (T-DXd) has demonstrated efficacy in HER2-positive and HER2-low breast cancer. Its main safety concern is interstitial lung disease, while clinically relevant hepatotoxicity is rarely reported. In our case report we describe a 49-year-old woman with HER2-positive advanced breast cancer that developed persistent grade 3 transaminase elevations after 2 cycles of T-DXd, refractory to corticosteroid treatment and requiring treatment discontinuation. This case underlines the unpredictable and idiosyncratic nature of T-DXd associated hepatotoxicity and the importance of liver function monitoring. Clinicians should consider DILI in patients with unexplained liver enzyme elevations during therapy. Further studies are needed to clarify mechanisms and risk factors.