ESR1 and triple-negative breast carcinoma: These four major subtypes are Luminal A (ER+ and/or PR+, HER2−, Ki-67 < 14%), luminal B (ER+ and/or PR+, HER2−, Ki-67 ≥ 14%; or ER+ and/or PR+, HER2+), HER2-enriched (ER−, PR−, HER2+), and triple negative breast cancer (TNBC; ER−, PR−, HER2−).