It adopts a constitutively open conformationthat readily forms homodimers or heterodimers with other receptorssuch as EGFR (ERBB1) and HER3 (ERBB3), leading to activation of downstreamsignaling cascades including the PI3K/AKT and MAPK pathways., Amplification or overexpression of HER2 occurs in approximately15–20% of breast cancers and is associated with increased tumoraggressiveness, higher recurrence rates, and reduced overall survival., The development of HER2-targeted monoclonal antibodies (mAbs) hassignificantly improved the outcomes in this patient population., The gene discussed is ERBB2; the disease is breast cancer.