A large population of them have breast cancer which does not overexpress HER2 receptors, those are clinically categorized as “HER2-negative.” The word “negative” does not mean that the tumor does not express any HER2 receptors; it actually means that the amount of the receptors is not enough for the anti-HER2 antibodies to be used as a treatment [13]. Here, ERBB2 is linked to breast cancer.