Abstract
BACKGROUND: Trastuzumab is a humanized monoclonal antibody approved for the treatment of breast cancer with HER2 amplification and/or overexpression. There are only 2 prior cases of trastuzumab-related hepatotoxicity reported in the literature. CASE REPORT: We report the case of a 60-year-old woman who was treated with trastuzumab for stage I invasive ductal carcinoma of the right breast. She successfully completed 6 months of therapy when an increase in liver transaminases was noted on routine examination. A full work-up for causes of acute and chronic liver disease was negative. After review of the patient's medication list, trastuzumab was thought to be the most likely culprit for the liver injury, based on timing of administration and rise in liver enzymes.