Among all breast cancers, approximately 75% of cases are classified as hormone receptor-positive (HR+; ER+ and/or the PR+) and HER2-negative (Howlader et al., 2014) and the statuses of ER and PR are predicted by the response to endocrine therapy (Ali, Buluwela & Coombes, 2011). The gene discussed is ERBB2; the disease is breast cancer.