Response to neoadjuvant chemotherapy (NAC) varies by estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) statuses, with responses being lower in ER-positive, HER2-negative cancers as compared with HER2-overexpressing or triple-negative tumors as evidenced by significantly lower pathological complete response (pCR) rate and objective response rate (ORR) [2, 3]. The gene discussed is ESR1; the disease is cancer.