Life-Saving Reduced Dose of Trastuzumab-Deruxtecan in Metastatic HER2-Low Metastatic Breast Cancer with Major Hepatic Insufficiency: A Case Report

Trastuzumab Deruxtecan has recently shown a good response in patients with HER2-low metastatic breast cancer, resulting in longer progression-free and overall survival.The most common adverse reactions are bone marrow suppression, cardiac, pulmonary, dermatological, gastrointestinal and hepatic (increased serum alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase and bilirubin, Cholestatic jaundice) toxicities.In severe hepatic impairment (total bilirubin >3 times ULN and any AST), there are no dosage adjustments provided in the manufacturer's labelling (a recommended dose has not been established) [1,2].The safety of this medication in liver failure is unknown.In the review of the literature, there is only one case report about a patient with metastatic HER2-positive breast cancer with liver failure and leptomeningeal metastases who was treated with dosereduced trastuzumab -Deruxtecan.With treatment, the patient's hyperbilirubinemia resolved, and she demonstrated a response on imaging.She was dose-escalated to full dose with minimal adverse events [3].We report here a rare case of a patient known to have HER2-low metastatic breast cancer with acute liver failure.She had received hormonal therapy and three lines of chemotherapy without improvement.Treatment with low dose Trastuzumab-Deruxtecan was started, and a significant improvement in liver function, liver metastases was observed after the first administration of Trastuzumab-Deruxtecan and normalization in 21 days after the second administration.