The development of the disease and treatment monitoring tools, however, are slowed down, and due to the biological complexity of BC, it is difficult to fully evaluate the treatment response, metastasis pattern, and clinical outcomes using the most common clinicopathological markers [estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and Ki-67] [6]. Here, ESR1 is linked to breast cancer.