As we all know, T-DM1 demonstrated a more favorable safety profile, with thrombocytopenia and hepatotoxicity being the main adverse events (AEs).In the KATHERINE trial, T-DM1 was used for residual early HER2-positive BC, and 5.7% of the patients developed Grade 3 or higher thrombocytopenia. This evidence concerns the gene ERBB2 and Thrombocytopenia.