The EGFR gene (a.k.a. ERBB1 and HER1) is located in the chromosomal region 7p11.2 and encodes a transmembrane glycoprotein acting as a cellular growth factor receptor. The protein belongs to the EGFR (epidermal growth factor receptor) subgroup of the RTK (receptor tyrosine kinase) superfamily also including ERBB2 (HER2), ERBB3 (HER3), and ERBB4 (HER4). Overexpression of EGFR has been shown in a number of tumor entities and is associated with poor prognosis. The epidermal growth factor receptor (EGFR) is one of the major oncogenes identified in a variety of human malignancies including breast cancer (BC). EGFR-mutations have been studied in lung cancer for some years and are established as important markers in guiding therapy with tyrosine kinase inhibitors (TKIs). EGFR copy number identified by FISH is thought to be a molecular predictor in neoplasms.