Breast cancer (BC) remains the most prevalentcancer worldwideand is a leading cause of cancer-related mortality among women.1 Currently, the classification and assessmentof BC primarily rely on tumor staging, grading, and several molecularbiomarkers, including estrogen receptor (ER), progesterone receptor(PgR), human epidermal growth factor receptor 2 (HER2), and Ki-67 (a proliferation marker). The gene discussed is ESR1; the disease is cancer.