ESR1 and breast cancer: The following molecular subtypes exist for breast cancer: Luminal A (ER+, HER2−, Ki67low, PgRhigh), Luminal B (ER+, HER2−, either Ki67high or PgRlow or ER+, HER2+, any Ki67, any PgR), Her2+ (HER2+, ER−, and PgR−), and triple negative cases (TNBC, HER2−, ER−, PgR−) [31].