ESR1 and breast cancer: Since then, studies with larger samples5,6,7,8,9,10,11,12,13,14,15 have been conducted; however, these studies had mixed findings, with some reporting worse prognosis among those with a family history of BC,5,6,7 some finding no significant difference,8,9,10,11,12 and some reporting that family history had a protective benefit for prognosis.13,14,15 Even less is known about whether the association differs across BC subtypes, such as ER-positive and ER-negative BC.