The immunohistochemical examination of the tumor cells showed positivity for the estrogen receptor (ER; Allred score, proportion score (PS) 4 + intensity score (IS) 2 = total score (TS) 6), and negative findings for the progesterone receptor (PgR; Allred score, PS 0 + IS 0 = TS 0) and HER2 (score 0). The gene discussed is ESR1; the disease is neoplasm.