MCF-7 is a luminal A subtype, estrogen receptor-positive (ER+), and considered less aggressive, while MDA-MB-231 represents the triple-negative breast cancer (TNBC) subtype, characterized by the absence of ER, PR, and HER2 expression, and is associated with higher aggressiveness, invasiveness, and poor prognosis [65,66]. Here, ESR1 is linked to triple-negative breast carcinoma.