ESR1 and breast cancer: Previous studies showed that BC in mammographically denser breasts are often more aggressive in terms of larger tumors and vascular invasion compared to cancers in less dense breasts [27, 29, 45]; the association between ER status [46, 47], PR status, HER2 status, lymph node involvement, mitotic index, and histological grade is incoherent [27, 29, 45].