In fact, epithelial proliferation is inversely associated with ER [34], and the frequency of Ki-67-expressing cells has been positively associated with increased risk of breast cancer, where high Ki-67+/low ER+ cell frequency was significantly associated with a 4.5-fold higher risk of breast cancer compared to low Ki-67+/high ER+ cell frequencies [15]. Here, ESR1 is linked to breast carcinoma.