ESR1 and cancer: Cancer can progress through the division of abnormal cells without ending or extending to other body tissues.1 Breast cancer (BC) is one of the predominant types of cancer in women, accounting for nearly 30% of all cancers, and has had a mortality rate of 14% in the last few years in India.2,3 BC is characterized by the expression of estrogen (ER), progesterone (PR) and human epidermal growth factor receptor-2 (HER-2).4 The receptors of BC cells determine the basis of targeted-treatment approaches and play a significant role in the prognosis and treatment of this disease.