In total, 46.4% of the patients (n = 1062) had a HER2-positive, 22.8% (n = 522) a triple-negative, and 32.1% (n = 750) a luminal-A-like/luminal B-like primary breast cancer (defined as estrogen receptor (ER) and/or progesterone receptor (PR) positive, HER2-negative). Here, ESR1 is linked to breast cancer.