While major advances in breast cancer treatment have been made over the last 20 years, it remains the leading cause of cancer-related death among women worldwide [1]; the most common breast cancer subtype is estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2–) cancer, accounting for approximately 70% of all cases [2–5]. The gene discussed is ERBB2; the disease is cancer.