ESR1 and breast cancer: The expression of key markers associated with proliferation (MKI67, PCNA, CCNB1, MYBL2, BUB1, CCND1), apoptosis (BCL2, CASP7, CASP8, CASP9, CASP3, BAX, APAF1), differentiation (CDH1, CD24, EPCAM, ESR1, NGFR, RUNX1), and breast cancer stemness (CD44, ITGA6, DNER, ALDH1A3, ABCG2, PROCR) was assessed.