ESR1 and breast neoplasm: Triple-negative breast cancer (TNBC) is a subtype of breast tumor that represents nearly 10–20% of all invasive breast cancers (BCs) and is characterized by deficient expression of the estrogen receptor (ER), progesterone (PR), and the human epidermal growth factor receptor 2 locus (HER2−) [1,2,3,4,5].