ERBB2 and Thrombocytopenia: Because the anti-HER2 antibody trastuzumab, as well as trastuzumab-containing ADCs such as T-DM1 are approved therapeutics, numerous studies have been performed to understand safety events associated with administration, i.e., cardiac toxicity with trastuzumab; thrombocytopenia and hepatoxicity with T-DM1.