T-DM1 has been the first FDA-approved ADC for solid tumors and consists of the anti-HER2 mAb trastuzumab conjugated via a stable linker to DM1, a microtubule inhibitor.2 Based on the results of the EMILIA and TH3RESA trials, T-DM1 became the standard of care for the treatment of HER2-positive metastatic breast cancer (mBC) in second line and beyond.24,25 Lately, T-DM1 has been established as standard treatment for patients with HER2-positive BC who do not achieve pathologic complete response (pCR) after neoadjuvant therapy (KATHERINE trial).26 Here, ERBB2 is linked to breast cancer.