ERBB2 and breast cancer: Given the results of the KATHERINE study which revealed improvements in invasive disease-free survival with the receipt of adjuvant trastuzumab emtansine (T-DM1) over trastuzumab alone in patients with residual disease following neoadjuvant chemotherapy and surgical resection [7], T-DM1 is increasingly being prescribed to early stage HER2 positive breast cancer patients [8].