ERBB2 and breast cancer: EGFR/ERBB1 overexpression is observed in 15–30% of breast cancer patients and is linked to tumor size and bad clinical outcomes [62] HER2 is also overexpressed in 20–30% of breast cancers but particularly in ductal carcinoma is attributed to its gene amplification, and results in constitutive activation of HER2 signaling, associated with poor clinical outcome and disease progression [52].