via multiple mechanisms
her2+ breast cancer cells have 2 million her2 receptors per cell, whereas normal cells have only 2 or 3, according to Dr Slamon
seems to be more effective vs. ER- than ER+ her2+ cell lines(SkBr3 vs BT474)
question is how safe it might be, but in at least one study in mice it seemed not to affect them adversely in any measurable way
Inhibition of phosphatidylcholine-specific phospholipase C downregulates HER2 overexpression on plasma membrane of breast cancer cells
http://breast-cancer-research.com/co...df/bcr2575.pdf