BC is classified into four main subtypes based on molecular characteristics and hormone receptor (HR) status assessed through immunohistochemistry (IHC): Luminal A (ER+, PR+, Ki67 <20%), Luminal B (ER+, PR+/−, HER2+/−, Ki67 >20%), HER2-overexpressing (HER2+), and Triple-negative BC (TNBC), which lacks expression of ER, PR, and HER2 [4]. Here, ESR1 is linked to breast cancer.