The patient underwentan ultrasound-guided core biopsy of the right breast mass with pathology revealinginvasive ductal carcinoma, grade 2, and positive for estrogen receptor (ER) 90%,progesterone receptor (PR) 1% to 5%, and human epidermal growth factor receptor 2positive, equivocal by immunohistochemistry, and positive by FISH (fluorescence insitu hybridization; Figure2a-c). The gene discussed is ESR1; the disease is breast ductal adenocarcinoma.