ESR1 and triple-negative breast carcinoma: On the basis of molecular subtyping [6], BCs are further classified in luminal A-like (ER+, PR+, HER2−, Ki67low), luminal B-like (ER+ and/or PR+, HER2+/−, Ki67low/high), HER2-enriched (ER−, PR−, HER2+, Ki67high) and basal-like [triple-negative breast cancer (TNBC); ER−, PR−, HER2−, Ki67high] [3].