Abstract: T-DM1 is a novel antibody-drug conjugate that has similar biological activity with that of trastuzumab. T-DM1 specifically delivers DM1, the effective anti-microtubule drug, into the cytoplasm of tumor cells with HER2 overexpression. The efficacy of T-DM1 monotherapy is better than lapatinib in combination with capecitabine and T-DM and is expected to become the standard second-line treatment for HER2-positive advanced breast cancer drugs. Clinical trials that compare T-DM1 with trastuzumab joint taxane as the first-line of treatment for advanced breast cancer trials are currently being performed. T-DM1 is a brand new anti-HER2 drug after trastuzumab. U.S. FDA already approved T-DM1 as a drug for the treatment of HER2-positive advanced breast cancer patients.