Furthermore, of the 4 HER proteins, only HER2 exhibited constitutive tyrosine phosphorylation upon overexpression.[32] Thus, HER2 overexpression in HER2-amplified breast cancer leads to the formation of multiple HER2 heterodimers and HER2 homodimers (HER2 is more biased toward the formation of heterodimers), resulting in stronger cellular signaling, enhancing the response to growth factors and malignant growth.[7,32,42]. The gene discussed is ERBB2; the disease is breast cancer.