ERBB2 and breast cancer: Following the success of T-DM1 in patients with HER2-positive breast cancer progressing on dual blockade with HER2 targeting antibodies trastuzumab and pertuzumab [28], the trastuzumab emtansine vs. taxane use for previously treated HER2-positive locally advanced or metastatic (la/m) gastric or gastro-oesophageal junction (GOJ) adenocarcinoma (GATSBY) trial evaluated the drug in a gastric cancer setting.