ERBB2 and breast cancer: In the HER2-overexpressing breast cancer cells, upon binding to HER2, T-DM1/HER2 complex is quickly internalized following by lysosomal degradation of antibody portion, leading to the intracellular release of payload, lys-MCC-DM1, to target microtubules and mediate apoptosis and cell death [12, 34, 35].