Eligible patients ( 18 years , left ventricular ejection fraction 50 % , Eastern Cooperative Oncology Group performance status 0-2 ) with progressive HER2-positive advanced breast cancer who had received two or more HER2-directed regimens in the advanced setting , including trastuzumab and lapatinib , and previous taxane therapy in any setting , were randomly assigned ( in a 2:1 ratio ) to trastuzumab emtansine ( 36 mg/kg intravenously every 21 days ) or physician 's choice using a permuted block randomisation scheme by an interactive voice and web response system .