Breast cancer accounts for about 20 % of female carcinomas. Expression of EGFR protein family receptors in breast carcinomas is quite common. ERBB-2 overexpression at protein level or gene amplification is present in approximately in one third of breast carcinomas and is associated with dismal prognosis. Pharmaceutical agents against ERBB-2 are currently used in breast cancer patients. The need for additional therapeutic strategies led to the development of a new class of agents called antibody-drug conjugates that were first evaluated in hematological malignancies. Trastuzumab emtansine (T-DM1) is the first immuno-conjugate that was tested and approved for the treatment of a solid tumor. In the present review, we will briefly update the rationale and clinical data of this agent and consider its perspectives in the treatment algorithm of breast cancer patients.