The molecular mechanisms of breast cancer are complex, but three main classes of breast cancer have been identified, namely progesterone positive (PR+) or estrogen receptor-positive (ER+), human epidermal receptor-positive (HER+), and triple negative breast cancer (TNBC), where TNBC lacks the ER, PR, and HER [3]. The gene discussed is ESR1; the disease is triple-negative breast carcinoma.