ERBB2 and breast cancer: Currently, patients with HER2+ BC, or TNBC and residual disease after NACT are treated with additional adjuvant therapies, such as trastuzumab emtansine (T-DM1) in the case of HER2+ BC and capecitabine in patients with TNBC, with novel experimental antibody-drug conjugates (ADCs) being currently evaluated; however, only a relatively small subset of these patients will undergo tumour relapse, thus exposing the majority of them to potentially toxic treatments.28