Estrogen receptor (ER) agonism leading to reproductive dysfunction (29), skewed sex ratios (52), and reduced survival (53); ER antagonism leading to reproductive dysfunction (30); modulation of adult Leydig cell function subsequent to estradiol activation in the fetal testis (67); increased dopaminergic activity leading to endometrial adenocarcinomas (112); anti‐estrogens and ovarian adenomas/granular cell tumors (165); early‐life ER activity leading to endometrial carcinoma in the mouse (167); ER activation leading to breast cancer (200). Here, ESR1 is linked to breast cancer.