Breast cancer is the most common cancer in women worldwide. The majority of deaths attributed to breast cancer are a result of metastatic disease, and 30% of early breast cancers (EBC) will develop distant disease. The 5-year survival of patients with metastatic disease is estimated at 23%. Breast cancer subtypes continue to be stratified histologically on oestrogen, progesterone and human epidermal growth factor-2 (HER2) receptor expression. HER2-positive breast cancers represent 25% of all breast cancer diagnoses. The therapies available for metastatic breast cancer (MBC) are expanding, in particular within the field of HER2-positive disease, with the approval of trastuzumab, pertuzumab, lapatinib and trastuzumab emtansine (TDM-1). Recently, TDM-1 has been shown to improve progression-free survival in HER2 MBC when compared to capecitabine and lapatinib in clinical studies. Its main toxicities are deranged liver function tests and thrombocytopenia. There have also been cases of acute liver failure. Therefore, its use in acute hepatic dysfunction, to our knowledge, has been neither studied nor reported. We report a patient with progressive HER2-positive MBC who had previously responded to multiple HER2-targeted therapies that presented with acute hepatic dysfunction. She was treated with dose-reduced TDM-1 safely, with clear evidence of rapid biochemical, clinical and radiological response. This allowed dose escalation of TDM-1, and the patient maintains an ongoing response.