It can be classified into three major subtypes based on receptor status: (1) hormone receptor-positive (HR+) BC, characterized by the presence of estrogen receptor (ER) and progesterone receptor (PR), (2) HER2-positive (HER2+), involving HER2 overexpression, and (3) triple-negative BC (TNBC), which lacks ER, PR, and HER2 expression [7]. The gene discussed is ESR1; the disease is breast cancer.