BC exhibited higher heterogeneity, according to the expression of human epidermal growth factor receptor 2 (HER2), progesterone receptor (PR), and estrogen receptor (ER), BC could be categorized into four main molecular subtypes of triple-negative breast cancer (TNBC), HER2-positive, Luminal B, and Luminal A (Fumagalli & Barberis, 2021). The gene discussed is ESR1; the disease is breast cancer.