When trastuzumab binds to the HER2 in breast cancer cells that overexpress the receptor, trastuzumab prevents growth factors from being able to bind to and stimulate the receptors, effectively blocking the growth of the cancer cells.
==== Targeted therapy ====In patients whose cancer expresses an over-abundance of the HER2 protein the drug trastuzumab (Herceptin ®) is used to block the HER2 protein in breast cancer cells slowing their growth.