Epidermal growth factor receptors in humans, including HER1, HER2, HER3, and HER4, are transmembrane receptor tyrosine kinases with partial homology that regulate cell growth and survival as well as adhesion, migration, and differentiation.(1) The HER2 gene is amplified in 25 to 30% of malignant breast tumors, and in these cases, the encoded protein is present at abnormally high levels in cells.(2). The gene discussed is ERBB2; the disease is breast cancer.