ERBB2 and cancer: We describe a 69-year-old woman with a history of human epidermal growth factor receptor 2 (HER2)-positive invasive breast cancer, treated with 15 cycles of trastuzumab emtansine (T-DM1) from January to October 2020. From the third cycle, she developed an increase in aminotransferase levels to three times the upper limit of normal, which normalized after discontinuation of T-DM1 due to cancer progression.