Cancer-derived exosomes from HER2-positive cancer cells carry trastuzumab-emtansine into cancer cells leading to growth inhibition and caspase activation.

T-DM1 binds to exosomes derived from HER2-positive cancer cells, and T-DM1 may be carried to other cancer cells via exosomes leading to reduced viability of the recipient cells. The results suggest a new mechanism of action for T-DM1, mediated by exosomes derived from HER2-positive cancer.