They have a complex mechanism of action and their effects are exerted in multiple ways, including HER2 protein downregulation, the prevention of HER2-containing heterodimer formation, the initiation of G1 cell cycle arrest by induction of the p27 tumor suppressor, the prevention of HER2 cleavage, the inhibition of angiogenesis, and the induction of immune mechanisms [55]. The gene discussed is ERBB2; the disease is neoplasm.