ERBB2 and neoplasm: However, when the overexpression of HER2 occurs, it can disrupt the dynamic balance of many cellular mechanisms and lead to uncontrollable tumor growth because: (i) Overexpression makes excessive HER2 receptors available to form extra heterocomplexes, (ii) HER2 may strengthen the affinity of ligand-binding for other receptors, (iii) HER2 might weaken the specificity of its heterodimerization partners, (iv) HER2-engaged dimerization can activate proliferation and survival, and (v) HER2-containing heterodimers may escape from the internalization or degradation of HER2 dimers.