ERBB2 and cancer: Targeted therapy is premised on blocking the dominant proliferative drivers of a given cancer, and it has translated into two major forms of treatment for breast cancers: (1) hormonal therapy for breast cancers that display receptors for estrogen and/or progesterone [3]; and (2) targeted therapy using monoclonal antibodies and small molecule inhibitors against ErbB2 for cancers that over-express this receptor protein tyrosine kinase [4].