The importance of ER-mediated growth and effect of fulvestrant treatment have also been found in exemestane-resistant cell lines derived from aromatase overexpressing MCF-7 cells (34), in MCF-7 breast tumor xenograft with letrozole-resistant aromatase overexpressing cells (50), and in the LTED model system (26). Here, CYP19A1 is linked to breast neoplasm.