They are classified into the following subtypes, luminal A, luminal B, HER2 positive, and basal type or triple negative breast cancer (TNBC), based on the presence of key protein receptors, namely estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) [10]. Here, ESR1 is linked to triple-negative breast carcinoma.