ERBB2 and breast carcinoma: Overexpression of HER2 is a negative prognostic factor in breast cancer and is found to be upregulated in 20% to 30% of all breast cancers; a patient diagnosed with HER2-positive breast cancer has more aggressive disease associated with an increased risk of metastases and shorter overall survival (Campiglio, Knyazev, & Ullrich, 1999; Gutierrez & Schiff, 2011).