Triple-negative breast cancer (TNBC) represents a heterogeneous subset of neoplasms defined by the absence of estrogen receptor (ER), progesterone receptor (PR) and Her2/neu, which accounts for approximately 15% of globally diagnosed breast cancers and which does not respond to hormonal therapy (such as tamoxifen or aromatase inhibitors) or therapies that target HER2 receptors [28-31]. This evidence concerns the gene ESR1 and breast cancer.