Association between HER2 status in residual disease and sensitivity to trastuzumab emtansine

I wish to congratulate Mamounas et al.1 for presenting additional exploratory safety and efficacy analyses in the KATHERINE study (NCT01772472) in which patients with residual invasive early breast cancer (EBC) after neoadjuvant chemotherapy (NACT) plus human epidermal growth factor receptor 2 (HER2)-targeted therapy had a 50% reduction in risk of recurrence or death with adjuvant trastuzumab emtansine (T-DM1) versus trastuzumab. They concluded that T-DM1 provides clinical benefit across patient subgroups, including small tumors and particularly high-risk tumors and does not increase the overall risk of central nervous system (CNS) recurrence.