Most breast cancers are estrogen-receptor positive (70% of breast cancers), followed by triple negative breast cancers (15–20% of breast cancers), and finally by human epidermal growth factor 2 positive breast cancers (10–15% of breast cancers) (Yeo and Guan, 2017; Waks and Winer, 2019). This evidence concerns the gene ESR1 and breast cancer.