This report describes the results of an analysis of patient-reported outcomes from EMILIA ( TDM4370g/BO21977 ) , a randomized phase 3 study of the antibody-drug conjugate trastuzumab emtansine ( T-DM1 ) versus capecitabine and lapatinib in human epidermal growth factor receptor 2 ( HER2 ) - positive locally advanced or metastatic breast cancer .