ESR1 and triple-negative breast carcinoma: Clinically, ER- and/or PR-positive and HER2-negative tumors are defined as luminal A, ER- and/or PR-positive, and HER-positive with high Ki67 expression is luminal B; HER2 overexpression with ER- and PR-negative is HER2-enriched; and triple-negative breast cancer (TNBC) is a subtype lacking ER, PR, and HER2 expression but with high Ki67 expression (Cancer Genome Atlas, 2012; Nagarajan and McArdle, 2018; Roswall et al., 2018).