In approximately 20% of breast cancers the human epidermal growth factor receptor 2 gene (c-erb-B2, ERRB2 or HER2), a member of the receptor tyrosine kinase 1 (RTK1) family, is amplified and overexpressed at the receptor level and these tumor characteristics are significantly associated with poor clinical outcome [2]. The gene discussed is ERBB2; the disease is breast cancer.