In the UK, it is recognised as the most common cancer with 55,000 new cases detected every year, and it is responsible for 7% of all cancer deaths [5]. ER-positive, HER2-negative, invasive breast cancer phenotype represents the most common subtype of breast cancer, accounting for 75% of all diagnosed invasive breast cancers [6]. The gene discussed is ERBB2; the disease is invasive breast carcinoma.