HER2‐positive BC: after accounting for baseline risk factors, E‐R for efficacy, demonstrated increases in T‐DM1 exposures are related to better efficacy (OS, PFS, ORR). E‐R for safety identified inverse trend for grade 3 or worse hepatotoxicity. No E‐R relationships identified for thrombocytopenia.a The gene discussed is ERBB2; the disease is Thrombocytopenia.