ERBB2 and breast cancer: These include tumors that express hormone receptors for estrogen (ER) and/or progesterone (PR) (the luminal phenotype), which include A and B subtypes, the latter of which predicts less positive outcomes; those that express HER2 (ERBB2) receptors; and those that express neither the hormone nor HER2 receptors (the “triple negative” (TNBC) phenotype), which is one of the most aggressive forms of breast cancer, exhibiting the highest mortality rates [3].