ESR1 and breast cancer: It is also the second common cause of cancer death in females.1-3 Breast cancer is the main cause of mortality in women aged 45 to 55.3-4 In 2013, nearly 234,000 women were diagnosed with breast cancer in US, 39,000 of who have died.5 Diagnostic evaluation of breast cancers is used commonly with immunohistochemistry (IHC) staining for three biomarkers of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor2 (HER2).4 One of the most challenging breast cancer types is TNBC.