Binds to tumor
) is a man-made antibody
that binds to cancer
cells if they express the her2 receptor. It acts like "seasoning" for the immune system, attracting immune cells which kill the tumor cells.
That's a simplistic explanation, because no one really understands what happens when Herceptin (trastuzumab) binds to tumor cells. There are many theories, but we know immune cells are necessary for it to work.