ESR1 and breast cancer: They select Gastrin Releasing Peptide Receptor (GRPR) gene which has recently been found to be associated with the estrogen receptor (ER) positivity [25] and gene Serpin Family A Member 6 (SERPINA6) which is identified as a marker of resistance to neoadjuvant chemotherapy in HER2-negative breast cancer [26] (HER2 is short for Human epidermal growth factor receptor 2).